Dark matter in the local group of galaxies

NASA Astrophysics Data System (ADS)

Morley, P. D.; Buettner, D. J.

We describe the neutrino flavor (e = electron, μ = muon, τ = tau) masses as mi=e,μ,τ = m + Δmi with |Δmi| m < 1 and probably |Δmi| m ≪ 1. The quantity m is the degenerate neutrino mass. Because neutrino flavor is not a quantum number, this degenerate mass appears in the neutrino equation-of-state [P. D. Morley and D. J. Buettner, Int. J. Mod. Phys. D (2014), doi:10.1142/s0218271815500042.]. We apply a Monte Carlo computational physics technique to the Local Group (LG) of galaxies to determine an approximate location for a Dark Matter embedding Condensed Neutrino Object (CNO) [P. D. Morley and D. J. Buettner, Int. J. Mod. Phys. D (2016), doi:10.1142/s0218271816500899.]. The calculation is based on the rotational properties of the only spiral galaxies within the LG: M31, M33 and the Milky Way. CNOs could be the Dark Matter everyone is looking for and we estimate the CNO embedding the LG to have a mass 5.17 × 1015 M⊙ and a radius 1.316 Mpc, with the estimated value of m ≃ 0.8 eV/c2. The up-coming KATRIN experiment [https://www.katrin.kit.edu.] will either be the definitive result or eliminate condensed neutrinos as a Dark Matter candidate.

Galaxy and Mass Assembly (GAMA): Impact of the Group Environment on Galaxy Star Formation

NASA Astrophysics Data System (ADS)

Barsanti, S.; Owers, M. S.; Brough, S.; Davies, L. J. M.; Driver, S. P.; Gunawardhana, M. L. P.; Holwerda, B. W.; Liske, J.; Loveday, J.; Pimbblet, K. A.; Robotham, A. S. G.; Taylor, E. N.

2018-04-01

We explore how the group environment may affect the evolution of star-forming galaxies. We select 1197 Galaxy And Mass Assembly groups at 0.05 ≤ z ≤ 0.2 and analyze the projected phase space (PPS) diagram, i.e., the galaxy velocity as a function of projected group-centric radius, as a local environmental metric in the low-mass halo regime 1012 ≤ (M 200/M ⊙) < 1014. We study the properties of star-forming group galaxies, exploring the correlation of star formation rate (SFR) with radial distance and stellar mass. We find that the fraction of star-forming group members is higher in the PPS regions dominated by recently accreted galaxies, whereas passive galaxies dominate the virialized regions. We observe a small decline in specific SFR of star-forming galaxies toward the group center by a factor ∼1.2 with respect to field galaxies. Similar to cluster studies, we conclude for low-mass halos that star-forming group galaxies represent an infalling population from the field to the halo and show suppressed star formation.

Galaxy Groups in the 2Mass Redshift Survey

NASA Astrophysics Data System (ADS)

Lu, Yi; Yang, Xiaohu; Shi, Feng; Mo, H. J.; Tweed, Dylan; Wang, Huiyuan; Zhang, Youcai; Li, Shijie; Lim, S. H.

2016-11-01

A galaxy group catalog is constructed from the 2MASS Redshift Survey (2MRS) with the use of a halo-based group finder. The halo mass associated with a group is estimated using a “GAP” method based on the luminosity of the central galaxy and its gap with other member galaxies. Tests using mock samples show that this method is reliable, particularly for poor systems containing only a few members. On average, 80% of all the groups have completeness \\gt 0.8, and about 65% of the groups have zero contamination. Halo masses are estimated with a typical uncertainty of ∼ 0.35 {dex}. The application of the group finder to the 2MRS gives 29,904 groups from a total of 43,246 galaxies at z≤slant 0.08, with 5286 groups having two or more members. Some basic properties of this group catalog is presented, and comparisons are made with other group catalogs in overlap regions. With a depth to z∼ 0.08 and uniformly covering about 91% of the whole sky, this group catalog provides a useful database to study galaxies in the local cosmic web, and to reconstruct the mass distribution in the local universe.

The NGC 1023 galaxy group: An anti-hubble flow?

NASA Astrophysics Data System (ADS)

Chernin, A. D.; Dolgachev, V. P.; Domozhilova, L. M.

2010-10-01

We discuss recently published data indicating that the nearby galaxy group NGC 1023 includes an inner, virialized, quasi-stationary component together with an outer component comprising a flow of dwarf galaxies falling toward the center of the system. The inner component is similar to the Local Group of galaxies, but the Local Group is surrounded by a receding set of dwarf galaxies forming the local Hubble flow, rather than a system of approaching dwarfs. This clear difference in the structures of these two systems, which are very similar in other respects, may be associated with the dark energy in which they are immersed. Self-gravity dominates in the inner component of the Local Group, while the anti-gravity created by the cosmic dark-energy background dominates in the surrounding Hubble flow. In contrast, self-gravity likewise dominates throughout the NGC 1023 Group, both in its central component and in the surrounding “anti-Hubble” flow. NGC 1023 as a whole is apparently in an ongoing state of formation and virialization. We expect that there exists a receding flow similar to the local Hubble flow at distances of 1.4-3 Mpc from the center of the group, where anti-gravity should become stronger than the gravity of the system.

A plane of high-velocity galaxies across the Local Group

NASA Astrophysics Data System (ADS)

Banik, Indranil; Zhao, Hongsheng

2018-01-01

We recently showed that several Local Group (LG) galaxies have much higher radial velocities (RVs) than predicted by a 3D dynamical model of the standard cosmological paradigm. Here, we show that six of these seven galaxies define a thin plane with root mean square thickness of only 101 kpc despite a widest extent of nearly 3 Mpc, much larger than the conventional virial radius of the Milky Way (MW) or M31. This plane passes within ∼70 kpc of the MW-M31 barycentre and is oriented so the MW-M31 line is inclined by 16° to it. We develop a toy model to constrain the scenario whereby a past MW-M31 flyby in Modified Newtonian Dynamics (MOND) forms tidal dwarf galaxies that settle into the recently discovered planes of satellites around the MW and M31. The scenario is viable only for a particular MW-M31 orbital plane. This roughly coincides with the plane of LG dwarfs with anomalously high RVs. Using a restricted N-body simulation of the LG in MOND, we show how the once fast-moving MW and M31 gravitationally slingshot test particles outwards at high speeds. The most distant such particles preferentially lie within the MW-M31 orbital plane, probably because the particles ending up with the highest RVs are those flung out almost parallel to the motion of the perturber. This suggests a dynamical reason for our finding of a similar trend in the real LG, something not easily explained as a chance alignment of galaxies with an isotropic or mildly flattened distribution (probability = 0.0015).

Local dark energy: HST evidence from the vicinity of the M81/M82 galaxy group

NASA Astrophysics Data System (ADS)

Chernin, A. D.; Karachentsev, I. D.; Kashibadze, O. G.; Makarov, D. I.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.

2007-10-01

The Hubble Space Telescope observations of the nearby galaxy group M81/M82 and its vicinity indicate that the dynamics of the expansion outflow around the group is dominated by the antigravity of the dark energy background. The local density of dark energy in the area is estimated to be near the global dark energy density or perhaps exactly equal to it. This conclusion agrees well with our previous results for the Local Group vicinity and the vicinity of the Cen A/M83 group.

Faint Dwarf Galaxies in Hickson Compact Group 90

NASA Astrophysics Data System (ADS)

Ordenes-Briceño, Y.; Taylor, M. A.; Puzia, T. H.; Muñoz, R. P.

2017-07-01

We report the discovery of a very diverse set of five low-surface brightness (LSB) dwarf galaxy candidates in Hickson Compact Group 90 (HCG 90) detected in deep U- and I-band images obtained with VLT/VIMOS. These are the first LSB dwarf galaxy candidates found in a compact group of galaxies, which share properties with dwarf galaxies found throughout the Local Volume and in nearby galaxy clusters such as Fornax. Among them, we find a pair of candidates with ˜2 kpc projected separation and a nucleated dwarf candidate, with nucleus size of reff≅46-63 pc.

LOCAL TADPOLE GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elmegreen, Debra Meloy; Putko, Joseph; Dewberry, Janosz

2012-05-10

Tadpole galaxies have a giant star-forming region at the end of an elongated intensity distribution. Here we use Sloan Digital Sky Survey data to determine the ages, masses, and surface densities of the heads and tails in 14 local tadpoles selected from the Kiso and Michigan surveys of UV-bright galaxies, and we compare them to tadpoles previously studied in the Hubble Ultra Deep Field. The young stellar mass in the head scales linearly with rest-frame galaxy luminosity, ranging from {approx}10{sup 5} M{sub Sun} at galaxy absolute magnitude U = -13 mag to 10{sup 9} M{sub Sun} at U = -20more » mag. The corresponding head surface density increases from several M {sub Sun} pc{sup -2} locally to 10-100 M{sub Sun} pc{sup -2} at high redshift, and the star formation rate (SFR) per unit area in the head increases from {approx}0.01 M{sub Sun} yr{sup -1} kpc{sup -2} locally to {approx}1 M{sub Sun} yr{sup -1} kpc{sup -2} at high z. These local values are normal for star-forming regions, and the increases with redshift are consistent with other cosmological SFRs, most likely reflecting an increase in gas abundance. The tails in the local sample look like bulge-free galaxy disks. Their photometric ages decrease from several Gyr to several hundred Myr with increasing z, and their surface densities are more constant than the surface densities of the heads. The far-outer intensity profiles in the local sample are symmetric and exponential. We suggest that most local tadpoles are bulge-free galaxy disks with lopsided star formation, perhaps from environmental effects such as ram pressure or disk impacts, or from a Jeans length comparable to half the disk size.« less

The Star Cluster System in the Local Group Starburst Galaxy IC 10

NASA Astrophysics Data System (ADS)

Lim, Sungsoon; Lee, Myung Gyoon

2015-05-01

We present a survey of star clusters in the halo of IC 10, a starburst galaxy in the Local Group, based on Subaru R-band images and NOAO Local Group Survey UBVRI images. We find five new star clusters. All of these star clusters are located far from the center of IC 10, while previously known star clusters are mostly located in the main body. Interestingly, the distribution of these star clusters shows an asymmetrical structure elongated along the east and southwest directions. We derive UBVRI photometry of 66 star clusters, including these new star clusters, as well as previously known star clusters. Ages of the star clusters are estimated from a comparison of their UBVRI spectral energy distribution with the simple stellar population models. We find that the star clusters in the halo are all older than 1 Gyr, while those in the main body have various ages, from very young (several Myr) to old (\\gt 1 Gyr). The young clusters (\\lt 10 Myr) are mostly located in the Hα emission regions and are concentrated on a small region at 2\\prime\\prime in the southeast direction from the galaxy center, while the old clusters are distributed in a wider area than the disk. Intermediate-age clusters (∼100 Myr) are found in two groups. One is close to the location of the young clusters and the other is at ∼ 4\\prime\\prime from the location of the young clusters. The latter may be related to past mergers or tidal interaction.

The statistical challenge of constraining the low-mass IMF in Local Group dwarf galaxies

NASA Astrophysics Data System (ADS)

El-Badry, Kareem; Weisz, Daniel R.; Quataert, Eliot

2017-06-01

We use Monte Carlo simulations to explore the statistical challenges of constraining the characteristic mass (mc) and width (σ) of a lognormal sub-solar initial mass function (IMF) in Local Group dwarf galaxies using direct star counts. For a typical Milky Way (MW) satellite (MV = -8), jointly constraining mc and σ to a precision of ≲ 20 per cent requires that observations be complete to ≲ 0.2 M⊙, if the IMF is similar to the MW IMF. A similar statistical precision can be obtained if observations are only complete down to 0.4 M⊙, but this requires measurement of nearly 100× more stars, and thus, a significantly more massive satellite (MV ˜ -12). In the absence of sufficiently deep data to constrain the low-mass turnover, it is common practice to fit a single-sloped power law to the low-mass IMF, or to fit mc for a lognormal while holding σ fixed. We show that the former approximation leads to best-fitting power-law slopes that vary with the mass range observed and can largely explain existing claims of low-mass IMF variations in MW satellites, even if satellite galaxies have the same IMF as the MW. In addition, fixing σ during fitting leads to substantially underestimated uncertainties in the recovered value of mc (by a factor of ˜4 for typical observations). If the IMFs of nearby dwarf galaxies are lognormal and do vary, observations must reach down to ˜mc in order to robustly detect these variations. The high-sensitivity, near-infrared capabilities of the James Webb Space Telescope and Wide-Field Infrared Survey Telescope have the potential to dramatically improve constraints on the low-mass IMF. We present an efficient observational strategy for using these facilities to measure the IMFs of Local Group dwarf galaxies.

What galaxy masses perturb the local cosmic expansion?

NASA Astrophysics Data System (ADS)

Peñarrubia, Jorge; Fattahi, Azadeh

2017-06-01

We use 12 cosmological N-body simulations of Local Group systems (the apostle models) to inspect the relation between the virial mass of the main haloes (Mvir,1 and Mvir,2), the mass derived from the relative motion of the halo pair (Mtim), and that inferred from the local Hubble flow (Mlhf). We show that within the spherical collapse model (SCM), the correspondence between the three mass estimates is exact, I.e. Mlhf = Mtim = Mvir,1 + Mvir,2. However, comparison with apostle simulations reveals that, contrary to what the SCM states, a relatively large fraction of the mass that perturbs the local Hubble flow and drives the relative trajectory of the main galaxies is not contained within Rvir, and that the amount of 'extravirial' mass tends to increase in galaxies with a slow accretion rate. In contrast, modelling the peculiar velocities around the Local Group returns an unbiased constraint on the virial mass ratio of the main galaxy pair. Adopting the outer halo profile found in N-body simulations, which scales as ρ ˜ R-4 at R ≳ Rvir, indicates that the galaxy masses perturbing the local Hubble flow roughly correspond to the asymptotically convergent (total) masses of the individual haloes. We show that estimates of Mvir based on the dynamics of tracers at R ≫ Rvir require a priori information on the internal matter distribution and the growth rate of the main galaxies, both of which are typically difficult to quantify.

On the recovery of the local group motion from galaxy redshift surveys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nusser, Adi; Davis, Marc; Branchini, Enzo, E-mail: adi@physics.technion.ac.il, E-mail: mdavis@berkeley.edu, E-mail: branchin@fis.uniroma3.it

2014-06-20

There is an ∼150 km s{sup –1} discrepancy between the measured motion of the Local Group (LG) of galaxies with respect to the cosmic microwave background and the linear theory prediction based on the gravitational force field of the large-scale structure in full-sky redshift surveys. We perform a variety of tests which show that the LG motion cannot be recovered to better than 150-200 km s{sup –1} in amplitude and within ≈10° in direction. The tests rely on catalogs of mock galaxies identified in the Millennium simulation using semi-analytic galaxy formation models. We compare these results to the K{sub s}more » = 11.75 Two-Mass Galaxy Redshift Survey, which provides the deepest and most complete all-sky spatial distribution of galaxies with spectroscopic redshifts available thus far. In our analysis, we use a new concise relation for deriving the LG motion and bulk flow from the true distribution of galaxies in redshift space. Our results show that the main source of uncertainty is the small effective depth of surveys like the Two-Mass Redshift Survey (2MRS), which prevents a proper sampling of the large-scale structure beyond ∼100 h {sup –1} Mpc. Deeper redshift surveys are needed to reach the 'convergence scale' of ≈250 h {sup –1} Mpc in a ΛCDM universe. Deeper surveys would also mitigate the impact of the 'Kaiser rocket' which, in a survey like 2MRS, remains a significant source of uncertainty. Thanks to the quiet and moderate density environment of the LG, purely dynamical uncertainties of the linear predictions are subdominant at the level of ∼90 km s{sup –1}. Finally, we show that deviations from linear galaxy biasing and shot noise errors provide a minor contribution to the total error budget.« less

LoCuSS: pre-processing in galaxy groups falling into massive galaxy clusters at z = 0.2

NASA Astrophysics Data System (ADS)

Bianconi, M.; Smith, G. P.; Haines, C. P.; McGee, S. L.; Finoguenov, A.; Egami, E.

2018-01-01

We report direct evidence of pre-processing of the galaxies residing in galaxy groups falling into galaxy clusters drawn from the Local Cluster Substructure Survey (LoCuSS). 34 groups have been identified via their X-ray emission in the infall regions of 23 massive ( = 1015 M⊙) clusters at 0.15 < z < 0.3. Highly complete spectroscopic coverage combined with 24 μm imaging from Spitzer allows us to make a consistent and robust selection of cluster and group members including star-forming galaxies down to a stellar mass limit of M⋆ = 2 × 1010 M⊙. The fraction fSF of star-forming galaxies in infalling groups is lower and with a flatter trend with respect to clustercentric radius when compared to the rest of the cluster galaxy population. At R ≈ 1.3 r200, the fraction of star-forming galaxies in infalling groups is half that in the cluster galaxy population. This is direct evidence that star-formation quenching is effective in galaxies already prior to them settling in the cluster potential, and that groups are favourable locations for this process.

The role of host galaxy for the environmental dependence of active nuclei in local galaxies

NASA Astrophysics Data System (ADS)

Davies, Richard I.; Hicks, E. K. S.; Erwin, P.; Burtscher, L.; Contursi, A.; Genzel, R.; Janssen, A.; Koss, M.; Lin, M.-Y.; Lutz, D.; Maciejewski, W.; Müller-Sánchez, F.; Orban de Xivry, G.; Ricci, C.; Riffel, R.; Riffel, R. A.; Rosario, D.; Schartmann, M.; Schnorr-Müller, A.; Shimizu, T.; Sternberg, A.; Sturm, E.; Storchi-Bergmann, T.; Tacconi, L.; Veilleux, S.

2017-04-01

We discuss the environment of local hard X-ray selected active galaxies, with reference to two independent group catalogues. We find that the fraction of these AGN in S0 host galaxies decreases strongly as a function of galaxy group size (halo mass) - which contrasts with the increasing fraction of galaxies of S0 type in denser environments. However, there is no evidence for an environmental dependence of AGN in spiral galaxies. Because most AGN are found in spiral galaxies, this dilutes the signature of environmental dependence for the population as a whole. We argue that the differing results for AGN in disc-dominated and bulge-dominated galaxies are related to the source of the gas fuelling the AGN, and so may also impact the luminosity function, duty cycle and obscuration. We find that there is a significant difference in the luminosity function for AGN in spiral and S0 galaxies, and tentative evidence for some difference in the fraction of obscured AGN.

STAR FORMATION IN DWARF GALAXIES OF THE NEARBY CENTAURUS A GROUP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cote, Stephanie; Draginda, Adam; Skillman, Evan D.

2009-10-15

We present H{alpha} narrow-band imaging of 17 dwarf irregular (dI) galaxies in the nearby Centaurus A Group. Although all large galaxies of the group are or recently have been through a period of enhanced star formation, the dIs have normal star formation rates (SFRs) and do not contain a larger fraction of dwarf starbursts than other nearby groups such as the Sculptor Group or the Local Group. Most of the galaxies in the group now have fairly accurately known distances, which enables us to obtain relative distances between dIs and larger galaxies of the group. We find that the dImore » SFRs do not depend on local environment, and in particular they do not show any correlation with the distance of the dI to the nearest large galaxy of the group. There is a clear morphology-density relation in the Centaurus A Group, similar to the Sculptor Group and Local Group, in the sense that dwarf ellipticals (dEs)/dwarf spheroidals (dSphs) tend to be at small distances from the more massive galaxies of the group, while dIs are on average at larger distances. We find four transition dwarfs in the Group, dwarfs that show characteristics of both dE/dSphs and dIs, and which contain cold gas but no current star formation. Interestingly, the transition dwarfs have an average distance to the more massive galaxies, which is intermediate between those of the dEs/dSphs and dIs and which is quite large: 0.54 {+-} 0.31 Mpc. This large distance poses some difficulty for the most popular scenarios proposed for transforming a dI into a dE/dSph (ram-pressure with tidal stripping or galaxy harassment). If the observed transition dwarfs are indeed missing links between dIs and dE/dSphs, their relative isolation makes it less likely to have been produced by these mechanisms. An inhomogeneous intergalactic medium containing higher density clumps would be able to ram-pressure strip the dIs at larger distances from the more massive galaxies of the group.« less

The Undergraduate ALFALFA Groups Project: Development of a Galaxy Environment Index

NASA Astrophysics Data System (ADS)

Crone, Mary; Turner, J.; ALFALFA Team

2010-01-01

The Undergraduate ALFALFA (Arecibo Legacy Fast ALFA) Team Groups Project is a collaborative undertaking of faculty and undergraduates at 8 institutions, aimed at investigating properties of galaxy groups surveyed by the ALFALFA blind HI survey. We present a galaxy environment index designed to reflect local density in the regions surrounding galaxy groups. These regions typically include hundreds of galaxies with optical and HI properties that can be compared with environment. For example, an 8x10 degree region surrounding the group MKW 11 includes 535 galaxies at the group redshift of 0.02, 139 of which are detected in HI. This work has been supported by NSF grants AST-0724918, AST-0725267, and AST-0725380.

Galaxy and Mass Assembly (GAMA): the GAMA galaxy group catalogue (G3Cv1)

NASA Astrophysics Data System (ADS)

Robotham, A. S. G.; Norberg, P.; Driver, S. P.; Baldry, I. K.; Bamford, S. P.; Hopkins, A. M.; Liske, J.; Loveday, J.; Merson, A.; Peacock, J. A.; Brough, S.; Cameron, E.; Conselice, C. J.; Croom, S. M.; Frenk, C. S.; Gunawardhana, M.; Hill, D. T.; Jones, D. H.; Kelvin, L. S.; Kuijken, K.; Nichol, R. C.; Parkinson, H. R.; Pimbblet, K. A.; Phillipps, S.; Popescu, C. C.; Prescott, M.; Sharp, R. G.; Sutherland, W. J.; Taylor, E. N.; Thomas, D.; Tuffs, R. J.; van Kampen, E.; Wijesinghe, D.

2011-10-01

Using the complete Galaxy and Mass Assembly I (GAMA-I) survey covering ˜142 deg2 to rAB= 19.4, of which ˜47 deg2 is to rAB= 19.8, we create the GAMA-I galaxy group catalogue (G3Cv1), generated using a friends-of-friends (FoF) based grouping algorithm. Our algorithm has been tested extensively on one family of mock GAMA lightcones, constructed from Λ cold dark matter N-body simulations populated with semi-analytic galaxies. Recovered group properties are robust to the effects of interlopers and are median unbiased in the most important respects. G3Cv1 contains 14 388 galaxy groups (with multiplicity ≥2), including 44 186 galaxies out of a possible 110 192 galaxies, implying ˜40 per cent of all galaxies are assigned to a group. The similarities of the mock group catalogues and G3Cv1 are multiple: global characteristics are in general well recovered. However, we do find a noticeable deficit in the number of high multiplicity groups in GAMA compared to the mocks. Additionally, despite exceptionally good local spatial completeness, G3Cv1 contains significantly fewer compact groups with five or more members, this effect becoming most evident for high multiplicity systems. These two differences are most likely due to limitations in the physics included of the current GAMA lightcone mock. Further studies using a variety of galaxy formation models are required to confirm their exact origin. The G3Cv1 catalogue will be made publicly available as and when the relevant GAMA redshifts are made available at .

Alignment of galaxies relative to their local environment in SDSS-DR8

NASA Astrophysics Data System (ADS)

Hirv, A.; Pelt, J.; Saar, E.; Tago, E.; Tamm, A.; Tempel, E.; Einasto, M.

2017-03-01

Aims: We study the alignment of galaxies relative to their local environment in SDSS-DR8 and, using these data, we discuss evolution scenarios for different types of galaxies. Methods: We defined a vector field of the direction of anisotropy of the local environment of galaxies. We summed the unit direction vectors of all close neighbours of a given galaxy in a particular way to estimate this field. We found the alignment angles between the spin axes of disc galaxies, or the minor axes of elliptical galaxies, and the direction of anisotropy. The distributions of cosines of these angles are compared to the random distributions to analyse the alignment of galaxies. Results: Sab galaxies show perpendicular alignment relative to the direction of anisotropy in a sparse environment, for single galaxies and galaxies of low luminosity. Most of the parallel alignment of Scd galaxies comes from dense regions, from 2...3 member groups and from galaxies with low luminosity. The perpendicular alignment of S0 galaxies does not depend strongly on environmental density nor luminosity; it is detected for single and 2...3 member group galaxies, and for main galaxies of 4...10 member groups. The perpendicular alignment of elliptical galaxies is clearly detected for single galaxies and for members of ≤10 member groups; the alignment increases with environmental density and luminosity. Conclusions: We confirm the existence of fossil tidally induced alignment of Sab galaxies at low z. The alignment of Scd galaxies can be explained via the infall of matter to filaments. S0 galaxies may have encountered relatively massive mergers along the direction of anisotropy. Major mergers along this direction can explain the alignment of elliptical galaxies. Less massive, but repeated mergers are possibly responsible for the formation of elliptical galaxies in sparser areas and for less luminous elliptical galaxies.

Isolated galaxies, pairs, and groups of galaxies

NASA Technical Reports Server (NTRS)

Kuneva, I.; Kalinkov, M.

1990-01-01

The authors searched for isolated galaxies, pairs and groups of galaxies in the CfA survey (Huchra et al. 1983). It was assumed that the distances to galaxies are given by R = V/H sub o, where H sub o = 100 km s(exp -1) Mpc(exp -1) and R greater than 6 Mpc. The searching procedure is close to those, applied to find superclusters of galaxies (Kalinkov and Kuneva 1985, 1986). A sphere with fixed radius r (asterisk) is described around each galaxy. The mean spatial density in the sphere is m. Let G (sup 1) be any galaxy and G (sup 2) be its nearest neighbor at a distance R sub 2. If R sub 2 exceeds the 95 percent quintile in the distribution of the distances of the second neighbors, then G (sup 1) is an isolated galaxy. Let the midpoint of G (sup 1) and G (sup 2) be O sub 2 and r sub 2=R sub 2/2. For the volume V sub 2, defined with the radius r sub 2, the density D sub 2 less than k mu, the galaxy G (sup 2) is a single one and the procedure for searching for pairs and groups, beginning with this object is over and we have to pass to another object. Here the authors present the groups - isolated and nonisolated - with n greater than 3, found in the CfA survey in the Northern galactic hemisphere. The parameters used are k = 10 and r (asterisk) = 5 Mpc. Table 1 contains: (1) the group number, (2) the galaxy, nearest to the multiplet center, (3) multiplicity n, (4) the brightest galaxy if it is not listed in (2); (5) and (6) are R.A. and Dec. (1950), (7) - mean distance D in Mpc. Further there are the mean density rho (8) of the multiplet (galaxies Mpc (exp -3), (9) the density rho (asterisk) for r (asterisk) = 5 Mpc and (10) the density rho sub g for the group with its nearest neighbor. The parenthesized digits for densities in the last three columns are powers of ten.

Identification of dusty massive stars in star-forming dwarf irregular galaxies in the Local Group with mid-IR photometry

NASA Astrophysics Data System (ADS)

Britavskiy, N. E.; Bonanos, A. Z.; Mehner, A.; Boyer, M. L.; McQuinn, K. B. W.

2015-12-01

Context. Increasing the statistics of spectroscopically confirmed evolved massive stars in the Local Group enables the investigation of the mass loss phenomena that occur in these stars in the late stages of their evolution. Aims: We aim to complete the census of luminous mid-IR sources in star-forming dwarf irregular (dIrr) galaxies of the Local Group. To achieve this we employed mid-IR photometric selection criteria to identify evolved massive stars, such as red supergiants (RSGs) and luminous blue variables (LBVs), by using the fact that these types of stars have infrared excess due to dust. Methods: The method is based on 3.6 μm and 4.5 μm photometry from archival Spitzer Space Telescope images of nearby galaxies. We applied our criteria to four dIrr galaxies: Pegasus, Phoenix, Sextans A, and WLM, selecting 79 point sources that we observed with the VLT/FORS2 spectrograph in multi-object spectroscopy mode. Results: We identified 13 RSGs, of which 6 are new discoveries, as well as two new emission line stars, and one candidate yellow supergiant. Among the other observed objects we identified carbon stars, foreground giants, and background objects, such as a quasar and an early-type galaxy that contaminate our survey. We use the results of our spectroscopic survey to revise the mid-IR and optical selection criteria for identifying RSGs from photometric measurements. The optical selection criteria are more efficient in separating extragalactic RSGs from foreground giants than mid-IR selection criteria, but the mid-IR selection criteria are useful for identifying dusty stars in the Local Group. This work serves as a basis for further investigation of the newly discovered dusty massive stars and their host galaxies. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 090.D-0009 and 091.D-0010.Appendix A is available in electronic form at http://www.aanda.org

Tidal stripping and the structure of dwarf galaxies in the Local Group

NASA Astrophysics Data System (ADS)

Fattahi, Azadeh; Navarro, Julio F.; Frenk, Carlos S.; Oman, Kyle A.; Sawala, Till; Schaller, Matthieu

2018-05-01

The shallow faint-end slope of the galaxy mass function is usually reproduced in Λ cold dark matter (ΛCDM) galaxy formation models by assuming that the fraction of baryons that turn into stars drops steeply with decreasing halo mass and essentially vanishes in haloes with maximum circular velocities Vmax < 20-30 km s-1. Dark-matter-dominated dwarfs should therefore have characteristic velocities of about that value, unless they are small enough to probe only the rising part of the halo circular velocity curve (i.e. half-mass radii, r1/2 ≪ 1 kpc). Many dwarfs have properties in disagreement with this prediction: they are large enough to probe their halo Vmax but their characteristic velocities are well below 20 km s-1. These `cold faint giants' (an extreme example is the recently discovered Crater 2 Milky Way satellite) can only be reconciled with our ΛCDM models if they are the remnants of once massive objects heavily affected by tidal stripping. We examine this possibility using the APOSTLE cosmological hydrodynamical simulations of the Local Group. Assuming that low-velocity-dispersion satellites have been affected by stripping, we infer their progenitor masses, radii, and velocity dispersions, and find them in remarkable agreement with those of isolated dwarfs. Tidal stripping also explains the large scatter in the mass discrepancy-acceleration relation in the dwarf galaxy regime: tides remove preferentially dark matter from satellite galaxies, lowering their accelerations below the amin ˜ 10-11 m s-2 minimum expected for isolated dwarfs. In many cases, the resulting velocity dispersions are inconsistent with the predictions from Modified Newtonian Dynamics, a result that poses a possibly insurmountable challenge to that scenario.

Scaling relations and the fundamental line of the local group dwarf galaxies

NASA Astrophysics Data System (ADS)

Woo, Joanna; Courteau, Stéphane; Dekel, Avishai

2008-11-01

We study the scaling relations between global properties of dwarf galaxies in the local group. In addition to quantifying the correlations between pairs of variables, we explore the `shape' of the distribution of galaxies in log parameter space using standardized principal component analysis, the analysis is performed first in the 3D structural parameter space of stellar mass M*, internal velocity V and characteristic radius R* (or surface brightness μ*). It is then extended to a 4D space that includes a stellar population parameter such as metallicity Z or star formation rate . We find that the local group dwarfs basically define a one-parameter `fundamental line' (FL), primarily driven by stellar mass, M*. A more detailed inspection reveals differences between the star formation properties of dwarf irregulars (dI's) and dwarf ellipticals (dE's), beyond the tendency of the latter to be more massive. In particular, the metallicities of dI's are typically lower by a factor of 3 at a given M* and they grow faster with increasing M*, showing a tighter FL in the 4D space for the dE's. The structural scaling relations of dI's resemble those of the more massive spirals, but the dI's have lower star formation rates for a given M* which also grow faster with increasing M*. On the other hand, the FL of the dE's departs from the fundamental plane of bigger ellipticals. While the one-parameter nature of the FL and the associated slopes of the scaling relations are consistent with the general predictions of supernova feedback from Dekel & Woo, the differences between the FL's of the dE's and the dI's remain a challenge and should serve as a guide for the secondary physical processes responsible for these two types.

Nearby groups of galaxies in the Hercules-Bootes constellations

NASA Astrophysics Data System (ADS)

Karachentsev, I. D.; Kashibadze, O. G.; Karachentseva, V. E.

2017-04-01

We consider a sample of 412 galaxies with radial velocities $V_{\\rm LG} < 2500$ km s$^{-1}$ situated in the sky region of ${\\rm RA}=13^h\\hspace{-0.4em}.\\,0$ ... $19^h\\hspace{-0.4em}.\\,0$, ${\\rm Dec}=+10^{\\circ}$ ... $+40^{\\circ}$ between the Local Void and the Supergalactic plane. One hundred and eighty-one of them have individual distance estimates. Peculiar velocities of the galaxies as a function of Supergalactic latitude SGB show signs of Virgocentric infall at $SGB < 10^{\\circ}$ and motion from the Local Void at $SGB > 60^{\\circ}$. A half of the Hercules-Bootes galaxies belong to 17 groups and 29 pairs, with the richest group around NGC5353. A typical group is characterized by the velocity dispersion of $67$ km s$^{-1}$, the harmonic radius of $182$ kpc, the stellar mass of $4.3 \\times10^{10} M_{\\odot}$ and the virial-to-stellar mass ratio of $32$. The binary galaxies have the mean radial velocity difference of $37$ km s$^{-1}$, the projected separation of $96$ kpc, the mean integral stellar mass of $2.6\\times 10^9 M_{\\odot}$ and the mean virial-to-stellar mass ratio of about $8$. The total dark-matter-to-stellar mass ratio in the considered sky region amounts to $37$ being almost the same as that in the Local Volume.

Properties of Galaxies and Groups: Nature versus Nurture

NASA Astrophysics Data System (ADS)

Niemi, Sami-Matias

2011-09-01

Due to the inherently nonlinear nature of gravity cosmological N-body simulations have become an invaluable tool when the growth of structure is being studied and modelled closer to the present epoch. Large simulations with high dynamical range have made it possible to model the formation and growth of cosmic structure with unprecedented accuracy. Moreover, galaxies, the basic building blocks of the Universe, can also be modelled in cosmological context. However, despite all the simulations and successes in recent decades, there are still many unanswered questions in the field of galaxy formation and evolution. One of the longest standing issue being the significance of the formation place and thus initial conditions to a galaxy's evolution in respect to environment, often formulated simply as "nature versus nurture" like in human development and psychology. Unfortunately, our understanding of galaxy evolution in different environments is still limited, albeit, for example, the morphology-density relation has shown that the density of the galaxy's local environment can affect its properties. Consequently, the environment should play a role in galaxy evolution, however despite the efforts, the exact role of the galaxy's local environment to its evolution remains open. This thesis introduction discusses briefly the background cosmology, cosmological N-body simulations and semi-analytical models. The second part is reserved for groups of galaxies, whether they are gravitationally bound, and what this may imply for galaxy evolution. The third part of the thesis concentrates on describing results of a case study of isolated field elliptical galaxies. The final chapter discusses another case study of luminous infra-red galaxies.

The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys

NASA Astrophysics Data System (ADS)

Sarbadhicary, Sumit; Badenes, Carles; Chomiuk, Laura; Maldonado, Jessica; Caprioli, Damiano; Heger, Mairead; Huizenga, Daniel

2018-01-01

Our understanding of the progenitors of many stellar species, such as supernovae, massive and low-mass He-burning stars, is limited because of many poorly constrained aspects of stellar evolution theory. For my dissertation, I have focused on using Local Group galaxy surveys to constrain stellar evolution scenarios by measuring delay-time distributions (DTD). The DTD is the hypothetical occurrence rate of a stellar object per elapsed time after a brief burst of star formation. It is the measured distribution of timescales on which stars evolve, and therefore serves as a powerful observational constraint on theoretical progenitor models. The DTD can be measured from a survey of stellar objects and a set of star-formation histories of the host galaxy, and is particularly effective in the Local Group, where high-quality star-formation histories are available from resolved stellar populations. I am currently calculating a SN DTD with supernova remnants (SNRs) in order to provide the strongest constraints on the progenitors of thermonuclear and core-collapse supernovae. However, most SNRs do not have reliable age measurements and their evolution depends on the ambient environment. For this reason, I wrote a radio light curve model of an SNR population to extract the visibility times and rates of supernovae - crucial ingredients for the DTD - from an SNR survey. The model uses observational constraints on the local environments from multi-wavelength surveys, accounts for missing SNRs and employs the latest models of shock-driven particle acceleration. The final calculation of the SN DTD in the Local Group is awaiting completion of a systematic SNR catalog from deep radio-continuum images, now in preparation by a group led by Dr. Laura Chomiuk. I have also calculated DTDs for the LMC population of RR Lyrae and Cepheid variables, which serve as important distance calibrators and stellar population tracers. We find that Cepheids can have delay-times between 10 Myrs - 1 Gyr

Modelling chemical abundance distributions for dwarf galaxies in the Local Group: the impact of turbulent metal diffusion

NASA Astrophysics Data System (ADS)

Escala, Ivanna; Wetzel, Andrew; Kirby, Evan N.; Hopkins, Philip F.; Ma, Xiangcheng; Wheeler, Coral; Kereš, Dušan; Faucher-Giguère, Claude-André; Quataert, Eliot

2018-02-01

We investigate stellar metallicity distribution functions (MDFs), including Fe and α-element abundances, in dwarf galaxies from the Feedback in Realistic Environment (FIRE) project. We examine both isolated dwarf galaxies and those that are satellites of a Milky Way-mass galaxy. In particular, we study the effects of including a sub-grid turbulent model for the diffusion of metals in gas. Simulations that include diffusion have narrower MDFs and abundance ratio distributions, because diffusion drives individual gas and star particles towards the average metallicity. This effect provides significantly better agreement with observed abundance distributions in dwarf galaxies in the Local Group, including small intrinsic scatter in [α/Fe] versus [Fe/H] of ≲0.1 dex. This small intrinsic scatter arises in our simulations because the interstellar medium in dwarf galaxies is well mixed at nearly all cosmic times, such that stars that form at a given time have similar abundances to ≲0.1 dex. Thus, most of the scatter in abundances at z = 0 arises from redshift evolution and not from instantaneous scatter in the ISM. We find similar MDF widths and intrinsic scatter for satellite and isolated dwarf galaxies, which suggests that environmental effects play a minor role compared with internal chemical evolution in our simulations. Overall, with the inclusion of metal diffusion, our simulations reproduce abundance distribution widths of observed low-mass galaxies, enabling detailed studies of chemical evolution in galaxy formation.

Local normal galaxies

NASA Technical Reports Server (NTRS)

Fichtel, Carl E.

1990-01-01

In the near future, high energy (E greater than 20 MeV) gamma ray astronomy offers the promise of a new means of examining the closest galaxies. Two and possibly three local galaxies, the Small and Large Magellanic Clouds and M31, should be visible to the high energy gamma ray telescope on the Gamma Ray Observatory, and the first should be seen by GAMMA-1. With the assumptions of adequate cosmic ray production and reasonable magnetic field strengths, both of which should likely be satisfied, specific predictions of the gamma ray emission can be made separating the concepts of the galactic and universal nature of cosmic rays. A study of the synchrotron radiation from the Large Magellanic Cloud (LMC) suggests that the cosmic ray density is similar to that in the local region of our galaxy, but not uniform. It is hoped the measurements will be able to verify this independent of assumptions about the magnetic fields in the LMC.

The Reddening law outside the local group galaxies: The case of NGC 7552 and NGC 5236

NASA Technical Reports Server (NTRS)

Kinney, Anne L.; Calzetti, Daniela; Bica, Eduardo; Storchi-Bergmann, Thaisa

1994-01-01

The dust reddening law from the UV to the near-IR for the extended regions of galaxies is here derived from the spectral distributions of the starburst spiral galaxies NGC 7552 and NGC 5236. The centers of these galaxies have similar absorption and emission line spectra, differing only if the strength of their interstellar lines and in the continuum distribution, with NGC 7552 appearing more reddened than NGC 5236. The disk of NGC 7552 is more inclined, and there is evidence that its center is observed through additional foreground dust and gas clouds, as compared to the center of NGC 5236. While the galaxies can be expected to have similar dust content, they are known to have different dust path lengths to our line of sight. Therefore, differences in the shape of the spectra can be attributed mainly to the effects of dust, allowing us to probe for the first time the properties of the reddening law outside the local group of galaxies. We derive the reddening law based on the optical depth of the emission line of H Alpha and H Beta and also based on the continuum distribtuion. We find that the optical depth from the emission line regions are about twice the optical depth of the continuum regions. Thus, dereddening a starburst galaxy by scaling the Milky Way reddening laws to optical depths obtained from the H Alpha/H Beta line ratio overcompensates for the effect of dust.

A unified model for age-velocity dispersion relations in Local Group galaxies: disentangling ISM turbulence and latent dynamical heating

NASA Astrophysics Data System (ADS)

Leaman, Ryan; Mendel, J. Trevor; Wisnioski, Emily; Brooks, Alyson M.; Beasley, Michael A.; Starkenburg, Else; Martig, Marie; Battaglia, Giuseppina; Christensen, Charlotte; Cole, Andrew A.; de Boer, T. J. L.; Wills, Drew

2017-12-01

We analyse age-velocity dispersion relations (AVRs) from kinematics of individual stars in eight Local Group galaxies ranging in mass from Carina (M* ∼ 106 M⊙) to M31 (M* ∼ 1011 M⊙). Observationally the σ versus stellar age trends can be interpreted as dynamical heating of the stars by giant molecular clouds, bars/spiral arms or merging subhaloes; alternatively the stars could have simply been born out of a more turbulent interstellar medium (ISM) at high redshift and retain that larger velocity dispersion till present day - consistent with recent integral field unit kinematic studies. To ascertain the dominant mechanism and better understand the impact of instabilities and feedback, we develop models based on observed star formation histories (SFHs) of these Local Group galaxies in order to create an evolutionary formalism that describes the ISM velocity dispersion due to a galaxy's evolving gas fraction. These empirical models relax the common assumption that the stars are born from gas that has constant velocity dispersion at all redshifts. Using only the observed SFHs as input, the ISM velocity dispersion and a mid-plane scattering model fits the observed AVRs of low-mass galaxies without fine tuning. Higher mass galaxies above Mvir ≳ 1011 M⊙ need a larger contribution from latent dynamical heating processes (for example minor mergers), in excess of the ISM model. Using the SFHs, we also find that supernovae feedback does not appear to be a dominant driver of the gas velocity dispersion compared to gravitational instabilities - at least for dispersions σ ≳ 25 km s-1. Together our results point to stars being born with a velocity dispersion close to that of the gas at the time of their formation, with latent dynamical heating operating with a galaxy mass-dependent efficiency. These semi-empirical relations may help constrain the efficiency of feedback and its impact on the physics of disc settling in galaxy formation simulations.

Galaxy And Mass Assembly (GAMA): Gas Fueling of Spiral Galaxies in the Local Universe. I. The Effect of the Group Environment on Star Formation in Spiral Galaxies

NASA Astrophysics Data System (ADS)

Grootes, M. W.; Tuffs, R. J.; Popescu, C. C.; Norberg, P.; Robotham, A. S. G.; Liske, J.; Andrae, E.; Baldry, I. K.; Gunawardhana, M.; Kelvin, L. S.; Madore, B. F.; Seibert, M.; Taylor, E. N.; Alpaslan, M.; Brown, M. J. I.; Cluver, M. E.; Driver, S. P.; Bland-Hawthorn, J.; Holwerda, B. W.; Hopkins, A. M.; Lopez-Sanchez, A. R.; Loveday, J.; Rushton, M.

2017-03-01

We quantify the effect of the galaxy group environment (for group masses of 1012.5-1014.0 M ⊙) on the current star formation rate (SFR) of a pure, morphologically selected sample of disk-dominated (I.e., late-type spiral) galaxies with redshift ≤0.13. The sample embraces a full representation of quiescent and star-forming disks with stellar mass M * ≥ 109.5 M ⊙. We focus on the effects on SFR of interactions between grouped galaxies and the putative intrahalo medium (IHM) of their host group dark matter halos, isolating these effects from those induced through galaxy-galaxy interactions, and utilizing a radiation transfer analysis to remove the inclination dependence of derived SFRs. The dependence of SFR on M * is controlled for by measuring offsets Δlog(ψ *) of grouped galaxies about a single power-law relation in specific SFR, {\\psi }* \\propto {M}* -0.45+/- 0.01, exhibited by non-grouped “field” galaxies in the sample. While a small minority of the group satellites are strongly quenched, the group centrals and a large majority of satellites exhibit levels of ψ * statistically indistinguishable from their field counterparts, for all M *, albeit with a higher scatter of 0.44 dex about the field reference relation (versus 0.27 dex for the field). Modeling the distributions in Δlog(ψ *), we find that (I) after infall into groups, disk-dominated galaxies continue to be characterized by a similar rapid cycling of gas into and out of their interstellar medium shown prior to infall, with inflows and outflows of ˜1.5-5 x SFR and ˜1-4 x SFR, respectively; and (II) the independence of the continuity of these gas flow cycles on M * appears inconsistent with the required fueling being sourced from gas in the circumgalactic medium on scales of ˜100 kpc. Instead, our data favor ongoing fueling of satellites from the IHM of the host group halo on ˜Mpc scales, I.e., from gas not initially associated with the galaxies upon infall. Consequently, the color

The star formation histories of local group dwarf galaxies. II. Searching for signatures of reionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.

We search for signatures of reionization in the star formation histories (SFHs) of 38 Local Group dwarf galaxies (10{sup 4} < M{sub *} < 10{sup 9} M{sub ☉}). The SFHs are derived from color-magnitude diagrams using archival Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. Only five quenched galaxies (And V, And VI, And XIII, Leo IV, and Hercules) are consistent with forming the bulk of their stars before reionization, when full uncertainties are considered. Observations of 13 of the predicted 'true fossils' identified by Bovill and Ricotti show that only two (Hercules and Leo IV) indicate star formation quenchedmore » by reionization. However, both are within the virial radius of the Milky Way and evidence of tidal disturbance complicates this interpretation. We argue that the late-time gas capture scenario posited by Ricotti for the low mass, gas-rich, and star-forming fossil candidate Leo T is observationally indistinguishable from simple gas retention. Given the ambiguity between environmental effects and reionization, the best reionization fossil candidates are quenched low mass field galaxies (e.g., KKR 25).« less

First-Ever Census of Variable Mira-Type Stars in Galaxy Outside the Local Group

NASA Astrophysics Data System (ADS)

2003-05-01

First-Ever Census of Variable Mira-Type Stars in Galaxy Outsidethe Local Group Summary An international team led by ESO astronomer Marina Rejkuba [1] has discovered more than 1000 luminous red variable stars in the nearby elliptical galaxy Centaurus A (NGC 5128) . Brightness changes and periods of these stars were measured accurately and reveal that they are mostly cool long-period variable stars of the so-called "Mira-type" . The observed variability is caused by stellar pulsation. This is the first time a detailed census of variable stars has been accomplished for a galaxy outside the Local Group of Galaxies (of which the Milky Way galaxy in which we live is a member). It also opens an entirely new window towards the detailed study of stellar content and evolution of giant elliptical galaxies . These massive objects are presumed to play a major role in the gravitational assembly of galaxy clusters in the Universe (especially during the early phases). This unprecedented research project is based on near-infrared observations obtained over more than three years with the ISAAC multi-mode instrument at the 8.2-m VLT ANTU telescope at the ESO Paranal Observatory . PR Photo 14a/03 : Colour image of the peculiar galaxy Centaurus A . PR Photo 14b/03 : Location of the fields in Centaurus A, now studied. PR Photo 14c/03 : "Field 1" in Centaurus A (visual light; FORS1). PR Photo 14d/03 : "Field 2" in Centaurus A (visual light; FORS1). PR Photo 14e/03 : "Field 1" in Centaurus A (near-infrared; ISAAC). PR Photo 14f/03 : "Field 2" in Centaurus A (near-infrared; ISAAC). PR Photo 14g/03 : Light variation of six variable stars in Centaurus A PR Photo 14h/03 : Light variation of stars in Centaurus A (Animated GIF) PR Photo 14i/03 : Light curves of four variable stars in Centaurus A. Mira-type variable stars Among the stars that are visible in the sky to the unaided eye, roughly one out of three hundred (0.3%) displays brightness variations and is referred to by astronomers as a

Westerbork Synthesis Radio Telescope HI Imaging of HI-selected Local Group Galaxy Candidates

NASA Astrophysics Data System (ADS)

Adams, Elizabeth A.; Cannon, J. M.; Oosterloo, T.; Giovanelli, R.; Haynes, M. P.

2014-01-01

The paucity of low mass galaxies in the Universe is a long-standing problem. We recently presented a set of isolated ultra-compact high velocity clouds (UCHVCs) identified within the dataset of the Arecibo Legacy Fast ALFA (ALFALFA) HI line survey that are consistent with representing low mass gas-bearing dark matter halos within the Local Group (Adams et al. 2013). At distances of ~1 Mpc, the UCHVCs have HI masses of ~10^5 Msun and indicative dynamical masses of ~10^7 Msun. The HI diameters of the UCHVCs range from 4' to 20', or 1 to 6 kpc at a distance of 1 Mpc. We have selected the most compact and isolated UCHVCs with the highest average column densities as representing the best galaxy candidates. Seven of these systems have been observed with WSRT to enable higher spatial resolution 40-60") studies of the HI distribution. The HI morphology revealed by the WSRT data offers clues to the environment of the UCHVCs, and velocity fields allow the underlying mass distribution to be constrained. The Cornell ALFALFA team is supported by NSF AST-1107390 and by the Brinson Foundation. JMC is supported by NSF grant AST-1211683.

Confirmation of Faint Dwarf Galaxies in the M81 Group

NASA Astrophysics Data System (ADS)

Chiboucas, Kristin; Jacobs, Bradley A.; Tully, R. Brent; Karachentsev, Igor D.

2013-11-01

We have followed up on the results of a 65 deg2 CFHT/MegaCam imaging survey of the nearby M81 Group searching for faint and ultra-faint dwarf galaxies. The original survey turned up 22 faint candidate dwarf members. Based on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as dwarf galaxy members of the group. Distances and stellar population characteristics are discussed for each. To a completeness limit of M_{r^{\\prime }} = -10, we find a galaxy luminosity function slope of -1.27 ± 0.04 for the M81 Group. In this region, there are now 36 M81 Group members known, including 4 blue compact dwarfs; 8 other late types including the interacting giants M81, NGC 3077, and M82; 19 early type dwarfs; and at least 5 potential tidal dwarf galaxies. We find that the dSph galaxies in M81 appear to lie in a flattened distribution, similar to that found for the Milky Way and M31. One of the newly discovered dSph galaxies has properties similar to the ultra-faint dwarfs being found in the Local Group with a size Re ~ 100 pc and total magnitude estimates M_{r^{\\prime }} = -6.8 and MI ~ -9.1.

LINER galaxy properties and the local environment

NASA Astrophysics Data System (ADS)

Coldwell, Georgina V.; Alonso, Sol; Duplancic, Fernanda; Mesa, Valeria

2018-05-01

We analyse the properties of a sample of 5560 low-ionization nuclear emission-line region (LINER) galaxies selected from SDSS-DR12 at low red shift, for a complete range of local density environments. The host LINER galaxies were studied and compared with a well-defined control sample of 5553 non-LINER galaxies matched in red shift, luminosity, morphology and local density. By studying the distributions of galaxy colours and the stellar age population, we find that LINERs are redder and older than the control sample over a wide range of densities. In addition, LINERs are older than the control sample, at a given galaxy colour, indicating that some external process could have accelerated the evolution of the stellar population. The analysis of the host properties shows that the control sample exhibits a strong relation between colours, ages and the local density, while more than 90 per cent of the LINERs are redder and older than the mean values, independently of the neighbourhood density. Furthermore, a detailed study in three local density ranges shows that, while control sample galaxies are redder and older as a function of stellar mass and density, LINER galaxies mismatch the known morphology-density relation of galaxies without low-ionization features. The results support the contribution of hot and old stars to the low-ionization emission although the contribution of nuclear activity is not discarded.

Statistical study of some Lee galaxy groups

NASA Astrophysics Data System (ADS)

Mohamed, Sabry A.; Fouad, Ahmed M.

2017-12-01

Compact groups of galaxies are systems of small number of galaxies close to each other. They are a good laboratory to study galaxy properties, such as structure, morphology and evolution which are affected by the environment and galaxy interactions. We applied the tree clustering technique (the Euclidean separation distance coefficients) to test the physical reality of groups and used certain criteria (Sabry et al., 2009) depending on the physical attributes of the galaxies. The sample of the data is the quintets groups of Lee compact groups of galaxies (Lee et al., 2004). It is based on a modified version of Hickson's criteria (Hickson, 1982). The results reveal the membership of each galaxy and how it is related to its group. The tables of groups and their members are included. Our results indicates that 12 Groups are real groups with real members while 18 Groups have one galaxy that has attribute discordant and should be discarded from its group.

Fossils of reionization in the local group

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gnedin, Nickolay Y.; /Fermilab /KICP, Chicago /Chicago U., EFI; Kravtsov, Andrey V.

We use a combination of high-resolution gas dynamics simulations of high-redshift dwarf galaxies and dissipationless simulations of a Milky Way sized halo to estimate the expected abundance and spatial distribution of the dwarf satellite galaxies that formed most of their stars around z {approx} 8 and evolved only little since then. Such galaxies can be considered as fossils of the reionization era, and studying their properties could provide a direct window into the early, pre-reionization stages of galaxy formation. We show that 5-15% of the objects existing at z {approx} 8 do indeed survive until the present in the MWmore » like environment without significant evolution. This implies that it is plausible that the fossil dwarf galaxies do exist in the Local Group. Because such galaxies form their stellar systems early during the period of active merging and accretion, they should have spheroidal morphology regardless of their current distance from the host galaxy. We show that both the expected luminosity function and spatial distribution of dark matter halos which are likely to host fossil galaxies agree reasonably well with the observed distributions of the luminous (L{sub V} > 10{sup 6} Lsun) Local Group fossil candidates near the host galaxy (d<200 kpc). However, the predicted abundance is substantially larger (by a factor of 2-3) for fainter galaxies (L{sub V} < 10{sup 6} Lsun) at larger distances (d>300 kpc). We discuss several possible explanations for this discrepancy.« less

Fermi Large Area Telescope observations of Local Group galaxies: detection of M 31 and search for M 33

DOE PAGES

Abdo, A. A.

2010-11-01

Context. Cosmic rays (CRs) can be studied through the galaxy-wide gamma-ray emission that they generate when propagating in the interstellar medium. The comparison of the diffuse signals from different systems may inform us about the key parameters in CR acceleration and transport. Aims. We aim to determine and compare the properties of the cosmic-ray-induced gamma-ray emission of several Local Group galaxies. Methods. We use 2 years of nearly continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to search for gamma-ray emission from M 31 and M 33. We compare the results with thosemore » for the Large Magellanic Cloud, the Small Magellanic Cloud, the Milky Way, and the starburst galaxies M 82 and NGC 253. Results. We detect a gamma-ray signal at 5σ significance in the energy range 200 MeV–20 GeV that is consistent with originating from M 31. The integral photon flux above 100 MeV amounts to (9.1 ± 1.9stat ± 1.0sys) × 10 -9 ph cm-2 s -1. We find no evidence for emission from M 33 and derive an upper limit on the photon flux >100 MeV of 5.1 × 10 -9 ph cm -2 s -1 (2σ). Comparing these results to the properties of other Local Group galaxies, we find indications of a correlation between star formation rate and gamma-ray luminosity that also holds for the starburst galaxies. Conclusions. The gamma-ray luminosity of M 31 is about half that of the Milky Way, which implies that the ratio between the average CR densities in M 31 and the Milky Way amounts to ξ = 0.35 ± 0.25. The observed correlation between gamma-ray luminosity and star formation rate suggests that the flux of M 33 is not far below the current upper limit from the LAT observations.« less

TWO LOCAL VOLUME DWARF GALAXIES DISCOVERED IN 21 cm EMISSION: PISCES A AND B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tollerud, Erik J.; Geha, Marla C.; Grcevich, Jana

2015-01-01

We report the discovery of two dwarf galaxies, Pisces A and B, from a blind 21 cm H I search. These were the only two galaxies found via optical imaging and spectroscopy of 22 H I clouds identified in the GALFA-H I survey as dwarf galaxy candidates. They have properties consistent with being in the Local Volume (<10 Mpc), and one has resolved stellar populations such that it may be on the outer edge of the Local Group (∼1 Mpc from M31). While the distance uncertainty makes interpretation ambiguous, these may be among the faintest star-forming galaxies known. Additionally, rough estimatesmore » comparing these galaxies to ΛCDM dark matter simulations suggest consistency in number density, implying that the dark matter halos likely to host these galaxies are primarily H I-rich. The galaxies may thus be indicative of a large population of dwarfs at the limit of detectability that are comparable to the faint satellites of the Local Group. Because they are outside the influence of a large dark matter halo to alter their evolution, these galaxies can provide critical anchors to dwarf galaxy formation models.« less

Observational properties of compact groups of galaxies

NASA Technical Reports Server (NTRS)

Hickson, Paul

1990-01-01

Compact groups are small, relatively isolated, systems of galaxies with projected separations comparable to the diameters of the galaxies themselves. Two well-known examples are Stephan's Quintet (Stephan, 1877) and Seyfert's Sextet (Seyfert 1948a,b). In groups such as these, the apparent space density of galaxies approaches 10(exp 6) Mpc(sub -3), denser even than the cores of rich clusters. The apparent unlikeliness of the chance occurrence of such tight groupings lead Ambartsumyan (1958, 1975) to conclude that compact groups must be physically dense systems. This view is supported by clear signs of galaxy interactions that are seen in many groups. Spectroscopic observations reveal that typical relative velocities of galaxies in the groups are comparable to their internal stellar velocities. This should be conducive to strong gravitational interactions - more so than in rich clusters, where galaxy velocities are typically much higher. This suggests that compact groups could be excellent laboratories in which to study galaxy interactions and their effects. Compact groups often contain one or more galaxies whose redshift differs greatly from those of the other group members. If these galaxies are at the same distance as the other members, either entire galaxies are being ejected at high velocities from these groups, or some new physical phenomena must be occurring. If their redshifts are cosmological, we must explain why so many discordant galaxies are found in compact groups. In recent years much progress has been made in addressing these questions. Here, the author discusses the current observational data on compact groups and their implications.

Local expansion flows of galaxies: quantifying acceleration effect of dark energy

NASA Astrophysics Data System (ADS)

Chernin, A. D.; Teerikorpi, P.

2013-08-01

The nearest expansion flow of galaxies observed around the Local group is studied as an archetypical example of the newly discovered local expansion flows around groups and clusters of galaxies in the nearby Universe. The flow is accelerating due to the antigravity produced by the universal dark energy background. We introduce a new acceleration measure of the flow which is the dimensionless ``acceleration parameter" Q (x) = x - x-2 depending on the normalized distance x only. The parameter is zero at the zero-gravity distance x = 1, and Q(x) ∝ x, when x ≫ 1. At the distance x = 3, the parameter Q = 2.9. Since the expansion flows have a self-similar structure in normalized variables, we expect that the result is valid as well for all the other expansion flows around groups and clusters of galaxies on the spatial scales from ˜ 1 to ˜ 10 Mpc everywhere in the Universe.

Interactions of galaxies outside clusters and massive groups

NASA Astrophysics Data System (ADS)

Yadav, Jaswant K.; Chen, Xuelei

2018-06-01

We investigate the dependence of physical properties of galaxies on small- and large-scale density environment. The galaxy population consists of mainly passively evolving galaxies in comparatively low-density regions of Sloan Digital Sky Survey (SDSS). We adopt (i) local density, ρ _{20}, derived using adaptive smoothing kernel, (ii) projected distance, r_p, to the nearest neighbor galaxy and (iii) the morphology of the nearest neighbor galaxy as various definitions of environment parameters of every galaxy in our sample. In order to detect long-range interaction effects, we group galaxy interactions into four cases depending on morphology of the target and neighbor galaxies. This study builds upon an earlier study by Park and Choi (2009) by including improved definitions of target and neighbor galaxies, thus enabling us to better understand the effect of "the nearest neighbor" interaction on the galaxy. We report that the impact of interaction on galaxy properties is detectable at least up to the pair separation corresponding to the virial radius of (the neighbor) galaxies. This turns out to be mostly between 210 and 360 h^{-1}kpc for galaxies included in our study. We report that early type fraction for isolated galaxies with r_p > r_{vir,nei} is almost ignorant of the background density and has a very weak density dependence for closed pairs. Star formation activity of a galaxy is found to be crucially dependent on neighbor galaxy morphology. We find star formation activity parameters and structure parameters of galaxies to be independent of the large-scale background density. We also exhibit that changing the absolute magnitude of the neighbor galaxies does not affect significantly the star formation activity of those target galaxies whose morphology and luminosities are fixed.

Galaxy Groups in HST/COS-SDSS Fields

NASA Astrophysics Data System (ADS)

Conway, Matthew; Hamill, Colin; Apala, Elizabeth; Scott, Jennifer

2018-01-01

We extend the results of a study of the sightlines of 45 low redshift quasars (0.06 < z < 0.85) observed by HST/COS that lie within the footprint of the Sloan Digital Sky Survey. We have used photometric data from the SDSS DR12, along with the known absorption characteristics of the intergalactic medium and circumgalactic medium, to identify the most probable galaxy matches to absorbers in the spectroscopic dataset. Here, we use an existing catalog of galaxy group candidates in the SDSS DR8 to identify galaxy groups within our HST/COS-SDSS fields that may show line of sight absorption due to an intergroup medium. To identify galaxy group candidates that lie within the impact parameter of our quasar fields (< 3 degrees), we calculate the angular separation between the quasar coordinates and the galaxy group centroid coordinates. We investigate differences in galaxy and absorber properties among the galaxy-absorber pairs likely arising in groups and those likely associated with individual field galaxies.

Dynamics of Galaxies in Compact Groups II.

NASA Astrophysics Data System (ADS)

Amram, P.; Mendes de Oliveira, C.

We show partial results of a program based on Fabry-Perot Hα velocity field data of compact groups taken at the ESO and the CFH 3.6m telescopes in order to analyze the kinematics of compact group galaxies. This project has three main goals: 1. determine the evolutionary stages of the groups; 2. search for tidal dwarf galaxies and 3. determine the Tully-Fisher relation for the group galaxies. We classify the compact groups studied so far into the following subclasses : (1) merging groups, (2) strongly interacting, (3) mildly interacting, (4) kinematically undisturbed and (5) false groups/single galaxy (details are given in the companion paper Mendes de Oliveira and Amram, 2000). We present examples of velocity fields of galaxies in compact groups that are in different evolutionary stages as classified from the kinematic disturbances. Spiral-only groups have often been considered chance alignments or groups in the very early stages of dynamical evolution. However, we find that the kinematics of the member galaxies for spiral-only groups in classes (1), (2) and (3) above display peculiarities which suggest that the galaxies know of the presence of their neighbors.

ROSAT observations of compact groups of galaxies

NASA Technical Reports Server (NTRS)

Pildis, Rachel A.; Bregman, Joel N.; Evrard, August E.

1995-01-01

We have systematically analyzed a sample of 13 new and archival ROSAT Position Sensitive Proportional Counter (PSPC) observations of compact groups of galaxies: 12 Hickson compact groups plus the NCG 2300 group. We find that approximately two-thirds of the groups have extended X-ray emission and, in four of these, the emission is resolved into diffuse emission from gas at a temperature of kT approximately 1 keV in the group potential. All but one of the groups with extended emission have a spiral fraction of less than 50%. The baryon fraction of groups with diffuse emission is 5%-19%, similar to the values in clusters of galaxies. However, with a single exception (HCG 62), the gas-to-stellar mass ratio in our groups has a median value near 5%, somewhat greater than the values for individual early-type galaxies and two orders of magnitude than in clusters of galaxies. The X-ray luminosities of individual group galaxies are comparable to those of similar field galaxies, although the L(sub X)-L(sub B) relation for early-type galaxies may be flatter in compact groups than in the field.

Galaxy And Mass Assembly (GAMA): The M-Z relation for galaxy groups

NASA Astrophysics Data System (ADS)

Lara-López, M. A.; Hopkins, A. M.; Robotham, A.; Owers, M. S.; Colless, M.; Brough, S.; Norberg, P.; Steele, O.; Taylor, E. N.; Thomas, D.

2013-04-01

The stellar mass and metallicity are among the fundamental parameters of galaxies. An understanding of the interplay between those properties as well as their environmental dependence will give us a general picture of the physics and feedback processes ongoing in groups of galaxies. We study the relationships and environmental dependencies between the stellar mass, and gas metallicity for more than 1900 galaxies in groups up to redshift 0.35 using the Galaxy And Mass Assembly (GAMA) survey. Using a control sample of more than 28 000 star-forming field galaxies, we find evidence for a decrement of the gas metallicity for galaxies in groups.

Mass dependent galaxy transformation mechanisms in the complex environment of SuperGroup Abell 1882

NASA Astrophysics Data System (ADS)

Sengupta, Aparajita

We present our data and results from panchromatic photometry and optical spectrometry of the nearest (extremely rich) filamentary large scale structure, SuperGroup Abell 1882. It is a precursor of a cluster and is an inevitable part of the narrative in the study of galaxy transformations. There has been strong empirical evidence over the past three decades that galaxy environment affects galaxy properties. Blue disky galaxies transform into red bulge-like galaxies as they traverse into the deeper recesses of a cluster. However, we have little insight into the story of galaxy evolution in the early stages of cluster formation. Besides, in relaxed clusters that have been studied extensively, several evolutionary mechanisms take effect on similar spatial and temporal scales, making it almost impossible to disentangle different local and global mechanisms. A SuperGroup on the other hand, has a shallower dark-matter potential. Here, the accreting galaxies are subjected to evolutionary mechanisms over larger time and spatial scales. This separates processes that are otherwise superimposed in rich cluster-filament interfaces. As has been found from cluster studies, galaxy color and morphology tie very strongly with local galaxy density even in a complex and nascent structure like Abell 1882. Our major results indicate that there is a strong dependence of galaxy transformations on the galaxy masses themselves. Mass- dependent evolutionary mechanisms affect galaxies at different spatial scales. The galaxy color also varies with radial projected distance from the assumed center of the structure for a constant local galaxy density, indicating the underlying large scale structure as a second order evolutionary driver. We have looked for clues to the types of mechanisms that might cause the transformations at various mass regimes. We have found the thoroughly quenched low mass galaxies confined to the groups, whereas there are evidences of intermediate-mass quenched galaxies

Detecting sub-lunar mass compact objects toward the Local Group galaxies

NASA Astrophysics Data System (ADS)

Inoue, Kaiki Taro

2018-01-01

By monitoring a large number of stars in the Local Group galaxies, we can detect nanolensing events by sub-lunar mass compact objects (SULCOs) such as primordial black holes (PBHs) and rogue (free-floating) dwarf planets in the Milky Way halo. In contarst to microlensing by stellar-mass objects, the finite-source size effect becomes important and the lensing time duration becomes shorter (∼10 1 - 4s). Using stars with V < 26 in M33 as sources, for one-night observation, we would be able to detect 10 3 - 4 nanolensing events caused by SULCOs in the Milky Way halo with a mass of 10-9M⊙ to 10-7M⊙ for sources with S/N > 5 if SULCOs constitute all the dark matter components. Moreover, we expect 10 1 - 2 events in which bright blue stars with S/N > 100 are weakly amplified due to lensing by SULCOs with a mass range of 10-11M⊙ to 10-9M⊙ . Thus the method would open a new window on SULCOs in the Milky Way halo that would otherwise not be observable.

Stellar populations in local star-forming galaxies

NASA Astrophysics Data System (ADS)

Perez-Gonzalez, P. G.

2003-11-01

The main goal of this thesis work is studying the main properties of the stellar populations embedded in a statistically complete sample of local active star-forming galaxies: the Universidad Complutense de Madrid (UCM) Survey of emission-line galaxies. This sample contains 191 local star-forming galaxies at an average redshift of 0.026. The survey was carried out using an objective-prism technique centered at the wavelength of the Halpha nebular emission-line (a common tracer of recent star formation). (continues)

Cosmic flow around local massive galaxies

NASA Astrophysics Data System (ADS)

Kashibadze, Olga G.; Karachentsev, Igor D.

2018-01-01

Aims: We use accurate data on distances and radial velocities of galaxies around the Local Group, as well as around 14 other massive nearby groups, to estimate their radius of the zero-velocity surface, R0, which separates any group against the global cosmic expansion. Methods: Our R0 estimate was based on fitting the data to the velocity field expected from the spherical infall model, including effects of the cosmological constant. The reported uncertainties were derived by a Monte Carlo simulation. Results: Testing various assumptions about a location of the group barycentre, we found the optimal estimates of the radius to be 0.91 ± 0.05 Mpc for the Local Group, and 0.93 ± 0.02 Mpc for a synthetic group stacked from 14 other groups in the Local Volume. Under the standard Planck model parameters, these quantities correspond to the total mass of the group (1.6 ± 0.2) × 1012M⊙. Thus, we are faced with the paradoxical result that the total mass estimate on the scale of R0 ≈ (3-4)Rvir is only 60% of the virial mass estimate. Anyway, we conclude that wide outskirts of the nearby groups do not contain a large amount of hidden mass outside their virial radius.

Galaxy groups in the low-redshift Universe

NASA Astrophysics Data System (ADS)

Lim, S. H.; Mo, H. J.; Lu, Yi; Wang, Huiyuan; Yang, Xiaohu

2017-09-01

We apply a halo-based group finder to four large redshift surveys, the 2MRS (Two Micron All-Sky Redshift Survey), 6dFGS (Six-degree Field Galaxy Survey), SDSS (Sloan Digital Sky Survey) and 2dFGRS (Two-degree Field Galaxy Redshift Survey), to construct group catalogues in the low-redshift Universe. The group finder is based on that of Yang et al. but with an improved halo mass assignment so that it can be applied uniformly to various redshift surveys of galaxies. Halo masses are assigned to groups according to proxies based on the stellar mass/luminosity of member galaxies. The performances of the group finder in grouping galaxies according to common haloes and in halo mass assignments are tested using realistic mock samples constructed from hydrodynamical simulations and empirical models of galaxy occupation in dark matter haloes. Our group finder finds ∼94 per cent of the correct true member galaxies for 90-95 per cent of the groups in the mock samples; the halo masses assigned by the group finder are un-biased with respect to the true halo masses, and have a typical uncertainty of ∼0.2 dex. The properties of group catalogues constructed from the observational samples are described and compared with other similar catalogues in the literature.

Undergraduate ALFALFA Team: Analysis of Spatially-Resolved Star-Formation in Nearby Galaxy Groups and Clusters

NASA Astrophysics Data System (ADS)

Finn, Rose; Collova, Natasha; Spicer, Sandy; Whalen, Kelly; Koopmann, Rebecca A.; Durbala, Adriana; Haynes, Martha P.; Undergraduate ALFALFA Team

2017-01-01

As part of the Undergraduate ALFALFA Team, we are conducting a survey of the gas and star-formation properties of galaxies in 36 groups and clusters in the local universe. The galaxies in our sample span a large range of galactic environments, from the centers of galaxy groups and clusters to the surrounding infall regions. One goal of the project is to map the spatial distribution of star-formation; the relative extent of the star-forming and stellar disks provides important information about the internal and external processes that deplete gas and thus drive galaxy evolution. We obtained wide-field H-alpha observations with the WIYN 0.9m telescope at Kitt Peak National Observatory for galaxies in the vicinity of the MKW11 and NRGb004 galaxy groups and the Abell 1367 cluster. We present a preliminary analysis of the relative size of the star-forming and stellar disks as a function of galaxy morphology and local galaxy density, and we calculate gas depletion times using star-formation rates and HI gas mass. We will combine these results with those from other UAT members to determine if and how environmentally-driven gas depletion varies with the mass and X-ray properties of the host group or cluster. This work has supported by NSF grants AST-0847430, AST-1211005 and AST-1637339.

Galaxy groups

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brent Tully, R.

2015-02-01

Galaxy groups can be characterized by the radius of decoupling from cosmic expansion, the radius of the caustic of second turnaround, and the velocity dispersion of galaxies within this latter radius. These parameters can be a challenge to measure, especially for small groups with few members. In this study, results are gathered pertaining to particularly well-studied groups over four decades in group mass. Scaling relations anticipated from theory are demonstrated and coefficients of the relationships are specified. There is an update of the relationship between light and mass for groups, confirming that groups with mass of a few times 10{supmore » 12}M{sub ⊙} are the most lit up while groups with more and less mass are darker. It is demonstrated that there is an interesting one-to-one correlation between the number of dwarf satellites in a group and the group mass. There is the suggestion that small variations in the slope of the luminosity function in groups are caused by the degree of depletion of intermediate luminosity systems rather than variations in the number per unit mass of dwarfs. Finally, returning to the characteristic radii of groups, the ratio of first to second turnaround depends on the dark matter and dark energy content of the universe and a crude estimate can be made from the current observations of Ω{sub matter}∼0.15 in a flat topology, with a 68% probability of being less than 0.44.« less

Glimpsing the imprint of local environment on the galaxy stellar mass function

NASA Astrophysics Data System (ADS)

Tomczak, Adam R.; Lemaux, Brian C.; Lubin, Lori M.; Gal, Roy R.; Wu, Po-Feng; Holden, Bradford; Kocevski, Dale D.; Mei, Simona; Pelliccia, Debora; Rumbaugh, Nicholas; Shen, Lu

2017-12-01

We investigate the impact of local environment on the galaxy stellar mass function (SMF) spanning a wide range of galaxy densities from the field up to dense cores of massive galaxy clusters. Data are drawn from a sample of eight fields from the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey. Deep photometry allow us to select mass-complete samples of galaxies down to 109 M⊙. Taking advantage of >4000 secure spectroscopic redshifts from ORELSE and precise photometric redshifts, we construct three-dimensional density maps between 0.55 < z < 1.3 using a Voronoi tessellation approach. We find that the shape of the SMF depends strongly on local environment exhibited by a smooth, continual increase in the relative numbers of high- to low-mass galaxies towards denser environments. A straightforward implication is that local environment proportionally increases the efficiency of (a) destroying lower mass galaxies and/or (b) growth of higher mass galaxies. We also find a presence of this environmental dependence in the SMFs of star-forming and quiescent galaxies, although not quite as strongly for the quiescent subsample. To characterize the connection between the SMF of field galaxies and that of denser environments, we devise a simple semi-empirical model. The model begins with a sample of ≈106 galaxies at zstart = 5 with stellar masses distributed according to the field. Simulated galaxies then evolve down to zfinal = 0.8 following empirical prescriptions for star-formation, quenching and galaxy-galaxy merging. We run the simulation multiple times, testing a variety of scenarios with differing overall amounts of merging. Our model suggests that a large number of mergers are required to reproduce the SMF in dense environments. Additionally, a large majority of these mergers would have to occur in intermediate density environments (e.g. galaxy groups).

The Dynamics of the Local Group in the Era of Precision Astrometry

NASA Astrophysics Data System (ADS)

Besla, Gurtina; Garavito-Camargo, Nicolas; Patel, Ekta

2018-06-01

Our understanding of the dynamics of our Local Group of galaxies has changed dramatically over the past few years owing to significant advancements in astrometry and our theoretical understanding of galaxy structure. New surveys now enable us to map the 3D structure of our Milky Way and the dynamics of tracers of its dark matter distribution, like globular clusters, satellite galaxies and streams, with unprecedented precision. Some results have met with controversy, challenging preconceived notions of the orbital dynamics of key components of the Local Group. I will provide an overview of this evolving picture of our Local Group and outline how we can test the cold dark matter paradigm in the era of Gaia, LSST and JWST.

The galaxy environment in GAMA G3C groups using the Kilo Degree Survey Data Release 3

NASA Astrophysics Data System (ADS)

Costa-Duarte, M. V.; Viola, M.; Molino, A.; Kuijken, K.; , L. Sodré, Jr.; Bilicki, M.; Brouwer, M. M.; Buddelmeijer, H.; Grado, A.; de Jong, J. T. A.; Napolitano, N.; Puddu, E.; Radovich, M.; Vakili, M.

2018-04-01

We aim to investigate the galaxy environment in GAMA Galaxy Groups Catalogue (G3C) using a volume-limited galaxy sample from the Kilo Degree Survey Data Release 3. The k-Nearest Neighbour technique is adapted to take into account the probability density functions (PDFs) of photometric redshifts in our calculations. This algorithm was tested on simulated KiDS tiles, showing its capability of recovering the relation between galaxy colour, luminosity and local environment. The characterization of the galaxy environment in G3C groups shows systematically steeper density contrasts for more massive groups. The red galaxy fraction gradients in these groups is evident for most of group mass bins. The density contrast of red galaxies is systematically higher at group centers when compared to blue galaxy ones. In addition, distinct group center definitions are used to show that our results are insensitive to center definitions. These results confirm the galaxy evolution scenario which environmental mechanisms are responsible for a slow quenching process as galaxies fall into groups and clusters, resulting in a smooth observed colour gradients in galaxy systems.

The hELENa project - I. Stellar populations of early-type galaxies linked with local environment and galaxy mass

NASA Astrophysics Data System (ADS)

Sybilska, A.; Lisker, T.; Kuntschner, H.; Vazdekis, A.; van de Ven, G.; Peletier, R.; Falcón-Barroso, J.; Vijayaraghavan, R.; Janz, J.

2017-09-01

We present the first in a series of papers in The role of Environment in shaping Low-mass Early-type Nearby galaxies (hELENa) project. In this paper, we combine our sample of 20 low-mass early types (dEs) with 258 massive early types (ETGs) from the ATLAS3D survey - all observed with the SAURON integral field unit - to investigate early-type galaxies' stellar population scaling relations and the dependence of the population properties on local environment, extended to the low-σ regime of dEs. The ages in our sample show more scatter at lower σ values, indicative of less massive galaxies being affected by the environment to a higher degree. The shape of the age-σ relations for cluster versus non-cluster galaxies suggests that cluster environment speeds up the placing of galaxies on the red sequence. While the scaling relations are tighter for cluster than for the field/group objects, we find no evidence for a difference in average population characteristics of the two samples. We investigate the properties of our sample in the Virgo cluster as a function of number density (rather than simple clustrocentric distance) and find that dE ages correlate with the local density such that galaxies in regions of lower density are younger, likely because they are later arrivals to the cluster or have experienced less pre-processing in groups, and consequently used up their gas reservoir more recently. Overall, dE properties correlate more strongly with density than those of massive ETGs, which was expected as less massive galaxies are more susceptible to external influences.

Evolved stars in the Local Group galaxies - II. AGB, RSG stars and dust production in IC10

NASA Astrophysics Data System (ADS)

Dell'Agli, F.; Di Criscienzo, M.; Ventura, P.; Limongi, M.; García-Hernández, D. A.; Marini, E.; Rossi, C.

2018-06-01

We study the evolved stellar population of the Local Group galaxy IC10, with the aim of characterizing the individual sources observed and to derive global information on the galaxy, primarily the star formation history and the dust production rate. To this aim, we use evolutionary sequences of low- and intermediate-mass (M < 8 M⊙) stars, evolved through the asymptotic giant branch phase, with the inclusion of the description of dust formation. We also use models of higher mass stars. From the analysis of the distribution of stars in the observational planes obtained with IR bands, we find that the reddening and distance of IC10 are E(B - V) = 1.85 mag and d = 0.77 Mpc, respectively. The evolved stellar population is dominated by carbon stars, that account for 40% of the sources brighter than the tip of the red giant branch. Most of these stars descend from ˜1.1 - 1.3 M⊙ progenitors, formed during the major epoch of star formation, which occurred ˜2.5 Gyr ago. The presence of a significant number of bright stars indicates that IC10 has been site of significant star formation in recent epochs and currently hosts a group of massive stars in the core helium-burning phase. Dust production in this galaxy is largely dominated by carbon stars; the overall dust production rate estimated is 7 × 10-6 M⊙/yr.

Dynamical theory of dense groups of galaxies

NASA Technical Reports Server (NTRS)

Mamon, Gary A.

1990-01-01

It is well known that galaxies associate in groups and clusters. Perhaps 40% of all galaxies are found in groups of 4 to 20 galaxies (e.g., Tully 1987). Although most groups appear to be so loose that the galaxy interactions within them ought to be insignificant, the apparently densest groups, known as compact groups appear so dense when seen in projection onto the plane of the sky that their members often overlap. These groups thus appear as dense as the cores of rich clusters. The most popular catalog of compact groups, compiled by Hickson (1982), includes isolation among its selection critera. Therefore, in comparison with the cores of rich clusters, Hickson's compact groups (HCGs) appear to be the densest isolated regions in the Universe (in galaxies per unit volume), and thus provide in principle a clean laboratory for studying the competition of very strong gravitational interactions. The $64,000 question here is then: Are compact groups really bound systems as dense as they appear? If dense groups indeed exist, then one expects that each of the dynamical processes leading to the interaction of their member galaxies should be greatly enhanced. This leads us to the questions: How stable are dense groups? How do they form? And the related question, fascinating to any theorist: What dynamical processes predominate in dense groups of galaxies? If HCGs are not bound dense systems, but instead 1D change alignments (Mamon 1986, 1987; Walke & Mamon 1989) or 3D transient cores (Rose 1979) within larger looser systems of galaxies, then the relevant question is: How frequent are chance configurations within loose groups? Here, the author answers these last four questions after comparing in some detail the methods used and the results obtained in the different studies of dense groups.

Globular clusters in high-redshift dwarf galaxies: a case study from the Local Group

NASA Astrophysics Data System (ADS)

Zick, Tom O.; Weisz, Daniel R.; Boylan-Kolchin, Michael

2018-06-01

We present the reconstructed evolution of rest-frame ultraviolet (UV) luminosities of the most massive Milky Way dwarf spheroidal satellite galaxy, Fornax, and its five globular clusters (GCs) across redshift, based on analysis of the stellar fossil record and stellar population synthesis modelling. We find that (1) Fornax's (proto-)GCs can generate 10-100 times more UV flux than the field population, despite comprising <˜{5} per cent of the stellar mass at the relevant redshifts; (2) due to their respective surface brightnesses, it is more likely that faint, compact sources in the Hubble Frontier Fields (HFFs) are GCs hosted by faint galaxies, than faint galaxies themselves. This may significantly complicate the construction of a galaxy UV luminosity function at z > 3. (3) GC formation can introduce order-of-magnitude errors in abundance matching. We also find that some compact HFF objects are consistent with the reconstructed properties of Fornax's GCs at the same redshifts (e.g. surface brightness, star formation rate), suggesting we may have already detected proto-GCs in the early Universe. Finally, we discuss the prospects for improving the connections between local GCs and proto-GCs detected in the early Universe.

Estimating the Turn-around Radii of Six Isolated Galaxy Groups in the Local Universe

NASA Astrophysics Data System (ADS)

Lee, Jounghun

2018-03-01

Estimates of the turn-around radii of six isolated galaxy groups in the nearby universe are presented. From the Tenth Data Release of the Sloan Digital Sky Survey, we first select those isolated galaxy groups at redshifts z ≤ 0.05 in the mass range [0.3–1] × {10}14 {h}-1 {M}ȯ whose nearest-neighbor groups are located at distances larger than 15 times their virial radii. Then, we search for a gravitationally interacting web-like structure around each isolated group, which appears as an inclined streak pattern in the anisotropic spatial distribution of the neighboring field galaxies. Out of 59 isolated groups, only seven are found to possess such web-like structures in their neighbor zones, but one of them turns out to be NGC 5353/4, whose turn-around radius was already measured in a previous work and was thus excluded from our analysis. Applying the Turn-around Radius Estimator algorithm devised by Lee et al. to the identified web-like structures of the remaining six target groups, we determine their turn-around radii and show that three out of the six targets have larger turn-around radii than the spherical bound limit predicted by Planck cosmology. We discuss possible sources of the apparent violations of the three groups, including the underestimated spherical bound limit due to the approximation of the turn-around mass by the virial mass.

V-V compact group of galaxies

NASA Technical Reports Server (NTRS)

Bahcall, N.

1984-01-01

A search for X-ray emission from five compact groups of galaxies with the Einstein Observatory revealed detections from three groups. Soft, extended X-ray emission was observed in Stephan's Quintet which is most likely caused by hot intracluster gas. This provides evidence for dynamical interaction among the group galaxies. X-ray emission from the group Arp 330 may also originate in hot intracluster gas. Stephan's Quintet and Arp 330 have the largest velocity dispersions among the groups studied suggesting a correlation between high velocity and the release (or properties) of hot gas. X-ray emission from Arp 318 may originate in its member galaxies.

Faint dwarf galaxies in Hickson Compact Group 90*

NASA Astrophysics Data System (ADS)

Ordenes-Briceño, Yasna; Taylor, Matthew A.; Puzia, Thomas H.; Muñoz, Roberto P.; Eigenthaler, Paul; Georgiev, Iskren Y.; Goudfrooij, Paul; Hilker, Michael; Lançon, Ariane; Mamon, Gary; Mieske, Steffen; Miller, Bryan W.; Peng, Eric W.; Sánchez-Janssen, Rubén

2016-12-01

We report the discovery of a very diverse set of five low-surface brightness (LSB) dwarf galaxy candidates in Hickson Compact Group 90 (HCG 90) detected in deep U- and I-band images obtained with Very Large Telescope/Visible Multi-Object Spectrograph. These are the first LSB dwarf galaxy candidates found in a compact group of galaxies. We measure spheroid half-light radii in the range 0.7 ≲ reff/kpc ≲ 1.5 with luminosities of -11.65 ≲ MU ≲ -9.42 and -12.79 ≲ MI ≲ -10.58 mag, corresponding to a colour range of (U - I)0 ≃ 1.1-2.2 mag and surface brightness levels of μU ≃ 28.1 mag arcsec-2 and μI ≃ 27.4 mag arcsec-2. Their colours and luminosities are consistent with a diverse set of stellar population properties. Assuming solar and 0.02 Z⊙ metallicities we obtain stellar masses in the range M*|Z⊙ ≃ 105.7 - 6.3 M⊙ and M_{*}|_{0.02 Z_{⊙} ≃ 10^{6.3-8} M_{⊙}. Three dwarfs are older than 1 Gyr, while the other two significantly bluer dwarfs are younger than ˜2 Gyr at any mass/metallicity combination. Altogether, the new LSB dwarf galaxy candidates share properties with dwarf galaxies found throughout the Local Volume and in nearby galaxy clusters such as Fornax. We find a pair of candidates with ˜2 kpc projected separation, which may represent one of the closest dwarf galaxy pairs found. We also find a nucleated dwarf candidate, with a nucleus size of reff ≃ 46-63 pc and magnitude MU, 0 = -7.42 mag and (U - I)0 = 1.51 mag, which is consistent with a nuclear stellar disc with a stellar mass in the range 104.9 - 6.5 M⊙.

EVOLUTION OF GALAXY GROUPS IN THE ILLUSTRIS SIMULATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raouf, Mojtaba; Khosroshahi, Habib G.; Dariush, A., E-mail: m.raouf@ipm.ir

We present the first study of the evolution of galaxy groups in the Illustris simulation. We focus on dynamically relaxed and unrelaxed galaxy groups representing dynamically evolved and evolving galaxy systems, respectively. The evolutionary state of a group is probed from its luminosity gap and separation between the brightest group galaxy and the center of mass of the group members. We find that the Illustris simulation overproduces galaxy systems with a large luminosity gap, known as fossil systems, in comparison to observations and the probed semi-analytical predictions. However, this simulation is just as successful as the probed semi-analytic model inmore » recovering the correlation between luminosity gap and offset of the luminosity centroid. We find evolutionary tracks based on luminosity gap that indicate that a group with a large luminosity gap is rooted in one with a small luminosity gap, regardless of the position of the brightest group galaxy within the halo. This simulation helps to explore, for the first time, the black hole mass and its accretion rate in galaxy groups. For a given stellar mass of the brightest group galaxies, the black hole mass is larger in dynamically relaxed groups with a lower rate of mass accretion. We find this to be consistent with the latest observational studies of radio activity in the brightest group galaxies in fossil groups. We also find that the intragalactic medium in dynamically evolved groups is hotter for a given halo mass than that in evolving groups, again consistent with earlier observational studies.« less

Galaxy collisions and shocks in compact groups

NASA Astrophysics Data System (ADS)

O'Sullivan, Ewan

2017-09-01

Evidence from IR, X-ray and HI studies suggests that low mass compact groups represent a key evolutionary stage in which shocks caused by galaxy interactions drive both the transformation of gas-rich spirals into early-type galaxies, and the build-up of the hot IGM. We have selected five groups where extensive multi-wavelength data shows violent ongoing galaxy interactions. We now propose to observe them with Chandra and XMM, searching for or confirming the presence of shocks in the X-ray IGM, measuring their strength and ability to heat cold gas, and examining the impact of galaxy/IGM interactions on galaxy transformation. Combined with our IR, CO, HI and optical IFU data, these observations will provide an exceptionally detailed view of this critical stage of galaxy and group evolution.

LOCAL TADPOLE GALAXIES: DYNAMICS AND METALLICITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanchez Almeida, J.; Munoz-Tunon, C.; Mendez-Abreu, J.

2013-04-10

Tadpole galaxies, with a bright peripheral clump on a faint tail, are morphological types unusual in the nearby universe but very common early on. Low mass local tadpoles were identified and studied photometrically in a previous work, which we complete here analyzing their chemical and dynamical properties. We measure H{alpha} velocity curves of seven local tadpoles, representing 50% of the initial sample. Five of them show evidence for rotation ({approx}70%), and a sixth target hints at it. Often the center of rotation is spatially offset with respect to the tadpole head (three out of five cases). The size and velocitymore » dispersion of the heads are typical of giant H II regions, and three of them yield dynamical masses in fair agreement with their stellar masses as inferred from photometry. In four cases the velocity dispersion at the head is reduced with respect to its immediate surroundings. The oxygen metallicity estimated from [N II] {lambda}6583/H{alpha} often shows significant spatial variations across the galaxies ({approx}0.5 dex), being smallest at the head and larger elsewhere. The resulting chemical abundance gradients are opposite to the ones observed in local spirals, but agrees with disk galaxies at high redshift. We interpret the metallicity variation as a sign of external gas accretion (cold-flows) onto the head of the tadpole. The galaxies are low-metallicity outliers of the mass-metallicity relationship. In particular, two of the tadpole heads are extremely metal poor, with a metallicity smaller than a tenth of the solar value. These two targets are also very young (ages smaller than 5 Myr). All these results combined are consistent with the local tadpole galaxies being disks in early stages of assembling, with their star formation sustained by accretion of external metal-poor gas.« less

Interacting Group of Galaxies Known as Stephan Quintet

NASA Image and Video Library

2005-05-05

This ultraviolet image from NASA Galaxy Evolution Explorer is of the interacting group of galaxies known as Stephan Quintet NGC 7317, NGC 7318A, NGC 7318B, NGC 7319, NGC 7320, lower left. Of the five galaxies in this tightly packed group, NGC 7320 (the large spiral in the group) is probably a foreground galaxy and not associated with the other four. The spiral galaxy in the upper right is NGC 7331. http://photojournal.jpl.nasa.gov/catalog/PIA07905

COS Views of Local Galaxies Approaching Primeval Conditions

NASA Astrophysics Data System (ADS)

Wofford, Aida

2014-10-01

We will use COS G160M+G185M to observe the cosmollogically important lines C IV 1548+1551 A, He II 1640 A, O III] 1661+1666 A, and C III] 1907+1909 A in the three closest most metal-poor blue compact dwarf galaxies known. These galaxies approach primeval insterstellar and stellar conditions. One of the galaxies has no existing spectroscopic coverage in the UV. Available spectroscopy of the most metal-poor galaxies in the local universe are scarce, inhomogeneous, mostly low spectral-resolution, and are either noisy in main UV lines or lack their coverage. The proposed spectral resolution of about 20 km/s represents an order of magnitude improvement over existing HST data and allows us to disentangle stellar, nebular, and/or shock components to the lines. The high-quality constraints obtained in the framework of this proposal will make it possible to assess the relative likelihood of new spectral models of star-forming galaxies from different groups, in the best possible way achievable with current instrumentation. This will ensure that the best possible studies of early chemical enrichment of the universe can be achieved. The proposed observations are necessary to minimize large existing systematic uncertainties in the determination of high-redshift galaxy properties that JWST was in large part designed to measure.

X-Ray Binaries in Local Analogs to the First Galaxies

NASA Astrophysics Data System (ADS)

Brorby, Matthew G.

2017-02-01

The focus of this dissertation is to investigate the effect of metallicity on high-mass X-ray binary (HMXB) formation and evolution as a means to understand the evolution of the early Universe (z > 6). Understanding the population and X-ray output of HMXBs are vital to modelling the heating and ionization morphology of the intergalactic medium during the epoch of reionization. Current X-ray instruments are unable to directly detect very high redshift HMXBs, making it impossible to constrain population sizes in this way. Instead certain local galaxies may be used as analogs to infer the properties of galaxies in the early Universe. These local analogs should have properties consistent with those expected for the first galaxies, such as low-metallicity, compact morphology, and intense recent star formation. I present an X-ray population study of 25 blue compact dwarf galaxies (BCD), using multiwavelength data and Bayesian analysis techniques. We find a significant enhancement of the HMXB population in low-metallicity environments and suggest the same may be true in the early Universe. I continue the investigation of HMXB populations in a sample of 10 moderate metallicity (Z ≥ 0.3, Z solar masses), local star-forming galaxies known as Lyman Break Analogs (LBAs). I find evidence of a LX-SFR-metallicity plane in the combined sample of BCDs, LBAs, and regular star-forming galaxies. Then I study a third type of local analog to early Universe galaxies, the Green Pea galaxies. These are a subclass of luminous compact galaxies (LCGs) which show strong [OIII]lambda5007A emission indicative of extreme, recent star-formation. This pilot study was carried out to look, for the first time in X-rays, at this recently established class of galaxies and use them to test the LX-SFR-metallicity plane. Determining the spectral properties of bright HMXBs in low-metallicity environments also has important implications for models of X-ray heating leading up to the Epoch of Reionization. I

The Impact of Star Formation Histories on Stellar Mass Estimation: Implications from the Local Group Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Zhang, Hong-Xin; Puzia, Thomas H.; Weisz, Daniel R.

2017-11-01

Building on the relatively accurate star formation histories (SFHs) and metallicity evolution of 40 Local Group (LG) dwarf galaxies derived from resolved color-magnitude diagram modeling, we carried out a comprehensive study of the influence of SFHs, metallicity evolution, and dust extinction on the UV-to-near-IR color-mass-to-light ratio (color-{log}{{{\\Upsilon }}}\\star (λ)) distributions and M ⋆ estimation of local universe galaxies. We find that (1) the LG galaxies follow color-{log}{{{\\Upsilon }}}\\star (λ) relations that fall in between the ones calibrated by previous studies; (2) optical color-{log}{{{\\Upsilon }}}\\star (λ) relations at higher [M/H] are generally broader and steeper; (3) the SFH “concentration” does not significantly affect the color-{log}{{{\\Upsilon }}}\\star (λ) relations; (4) light-weighted ages < {age}{> }λ and metallicities < [{{M}}/{{H}}]{> }λ together constrain {log}{{{\\Upsilon }}}\\star (λ) with uncertainties ranging from ≲0.1 dex for the near-IR up to 0.2 dex for the optical passbands; (5) metallicity evolution induces significant uncertainties to the optical but not near-IR {{{\\Upsilon }}}\\star (λ) at a given < {age}{> }λ and < [{{M}}/{{H}}]{> }λ ; (6) the V band is the ideal luminance passband for estimating {{{\\Upsilon }}}\\star (λ) from single colors, because the combinations of {{{\\Upsilon }}}\\star (V) and optical colors such as B - V and g - r exhibit the weakest systematic dependences on SFHs, metallicities, and dust extinction; and (7) without any prior assumption on SFHs, M ⋆ is constrained with biases ≲0.3 dex by the optical-to-near-IR SED fitting. Optical passbands alone constrain M ⋆ with biases ≲0.4 dex (or ≲0.6 dex) when dust extinction is fixed (or variable) in SED fitting. SED fitting with monometallic SFH models tends to underestimate M ⋆ of real galaxies. M ⋆ tends to be overestimated (or underestimated) at the youngest (or oldest) < {age}{> }{mass}.

The Local Group: the ultimate deep field

NASA Astrophysics Data System (ADS)

Boylan-Kolchin, Michael; Weisz, Daniel R.; Bullock, James S.; Cooper, Michael C.

2016-10-01

Near-field cosmology - using detailed observations of the Local Group and its environs to study wide-ranging questions in galaxy formation and dark matter physics - has become a mature and rich field over the past decade. There are lingering concerns, however, that the relatively small size of the present-day Local Group (˜2 Mpc diameter) imposes insurmountable sample-variance uncertainties, limiting its broader utility. We consider the region spanned by the Local Group's progenitors at earlier times and show that it reaches 3 arcmin ≈ 7 comoving Mpc in linear size (a volume of ≈350 Mpc3) at z = 7. This size at early cosmic epochs is large enough to be representative in terms of the matter density and counts of dark matter haloes with Mvir(z = 7) ≲ 2 × 109 M⊙. The Local Group's stellar fossil record traces the cosmic evolution of galaxies with 103 ≲ M⋆(z = 0)/M⊙ ≲ 109 (reaching M1500 > -9 at z ˜ 7) over a region that is comparable to or larger than the Hubble Ultra-Deep Field (HUDF) for the entire history of the Universe. In the JWST era, resolved stellar populations will probe regions larger than the HUDF and any deep JWST fields, further enhancing the value of near-field cosmology.

The Milky Way, the Local Group & the IR Tully-Fisher Diagram

NASA Technical Reports Server (NTRS)

Malhotra, S.; Spergel, D.; Rhoads, J.; Li, J.

1996-01-01

Using the near infrared fluxes of local group galaxies derived from Cosmic Background Explorer/Diffuse Infrared Background Experiment band maps and published Cepheid distances, we construct Tully-Fisher diagrams for the Local Group.

Redshift differences of galaxies in nearby groups

NASA Technical Reports Server (NTRS)

Harrison, E. R.

1975-01-01

It is reported that galaxies in nearby groups exhibit anomalous nonvelocity redshifts. In this discussion, (1) four classes of nearby groups of galacies are analyzed, and no significant nonvelocity redshift effect is found; and (2) it is pointed out that transverse velocities (i.e., velocities transverse to the line of sight of the main galaxy, or center of mass) contribute components to the redshift measurements of companion galaxies. The redshifts of galaxies in nearby groups of appreciable angular size are considerably affected by these velocity projection effects. The transverse velocity contributions average out in rich, isotropic groups, and also in large samples of irregular groups of low membership, as in the four classes referred to in (1), but can introduce apparent discrepancies in small samples (as studied by Arp) of nearby groups of low membership.

New Members in the Galaxy Group Around Giant Radio Galaxy DA 240

NASA Astrophysics Data System (ADS)

Chen, Ru-Rong; Peng, Bo; Strom, Richard

2018-05-01

With new spectroscopic observations of group candidates around the giant radio galaxy DA 240, we have identified five new group members, increasing the number to twenty-five. While all the new members are located some distance from the host galaxy, two of them lie in one of the radio lobes, and the rest are found at a distance from the radio components. The new group members reinforce our earlier conclusion that the distribution of the DA 240 group with respect to the radio lobes is unusual among giant radio galaxy host environments.

A classification of the galaxy groups

NASA Technical Reports Server (NTRS)

Anosova, Joanna P.

1990-01-01

A statistical criterion has been proposed to reveal the random and physical clusterings among stars, galaxies and other objects. This criterion has been applied to the galaxy triples of the list by Karachentseva, Karaschentsev and Scherbanovsky, and the double galaxies of the list by Dahari where the primary components are the Seyfert galaxies. The confident physical, probable physical, probable optical and confident optical groups have been identified. The limit difference of radial velocities of components for the confident physical multiple galaxies has also been estimated.

Andromeda Galaxy

NASA Image and Video Library

2003-12-10

This image is from NASA Galaxy Evolution Explorer is an observation of the large galaxy in Andromeda, Messier 31. The Andromeda galaxy is the most massive in the local group of galaxies that includes our Milky Way.

The galaxy luminosity function around groups

NASA Astrophysics Data System (ADS)

González, R. E.; Padilla, N. D.; Galaz, G.; Infante, L.

2005-11-01

We present a study on the variations of the luminosity function of galaxies around clusters in a numerical simulation with semi-analytic galaxies, attempting to detect these variations in the 2dF Galaxy Redshift Survey. We subdivide the simulation box into equal-density regions around clusters, which we assume can be achieved by selecting objects at a given normalized distance (r/rrms, where rrms is an estimate of the halo radius) from the group centre. The semi-analytic model predicts important variations in the luminosity function out to r/rrms~= 5. In brief, variations in the mass function of haloes around clusters (large dark matter haloes with M > 1012h-1Msolar) lead to cluster central regions that present a high abundance of bright galaxies (high M* values) as well as low-luminosity galaxies (high α) at r/rrms~= 3 there is a lack of bright galaxies, which shows the depletion of galaxies in the regions surrounding clusters (minimum in M* and α), and a tendency to constant luminosity function parameters at larger cluster-centric distances. We take into account the observational biases present in the real data by reproducing the peculiar velocity effect on the redshifts of galaxies in the simulation box, and also by producing mock catalogues. We find that excluding from the analysis galaxies which in projection are close to the centres of the groups provides results that are qualitatively consistent with the full simulation box results. When we apply this method to mock catalogues of the 2dF Galaxy Redshift Survey (2dFGRS) and the 2PIGG catalogue of groups, we find that the variations in the luminosity function are almost completely erased by the Finger of God effect; only a lack of bright galaxies at r/rrms~= 3 can be marginally detected in the mock catalogues. The results from the real 2dFGRS data show a clearer detection of a dip in M* and α for r/rrms= 3, consistent with the semi-analytic predictions.

X-ray-selected galaxy groups in Boötes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vajgel, Bruna; Lopes, Paulo A. A.; Jones, Christine

2014-10-10

We present the X-ray and optical properties of the galaxy groups selected in the Chandra X-Boötes survey. We used follow-up Chandra observations to better define the group sample and their X-ray properties. Group redshifts were measured from the AGN and Galaxy Evolution Survey spectroscopic data. We used photometric data from the NOAO Deep Wide Field Survey to estimate the group richness (N {sub gals}) and the optical luminosity (L {sub opt}). Our final sample comprises 32 systems at z < 1.75 with 14 below z = 0.35. For these 14 systems, we estimate velocity dispersions (σ {sub gr}) and performmore » a virial analysis to obtain the radii (R {sub 200} and R {sub 500}) and total masses (M {sub 200} and M {sub 500}) for groups with at least 5 galaxy members. We use the Chandra X-ray observations to derive the X-ray luminosity (L{sub X} ). We examine the performance of the group properties σ{sub gr}, L {sub opt}, and L{sub X} , as proxies for the group mass. Understanding how well these observables measure the total mass is important to estimate how precisely the cluster/group mass function is determined. Exploring the scaling relations built with the X-Boötes sample and comparing these with samples from the literature, we find a break in the L{sub X} -M {sub 500} relation at approximately M {sub 500} = 5 × 10{sup 13} M {sub ☉} (for M {sub 500} > 5 × 10{sup 13} M {sub ☉}, M{sub 500}∝L{sub X}{sup 0.61±0.02}, while for M {sub 500} ≤ 5 × 10{sup 13} M {sub ☉}, M{sub 500}∝L{sub X}{sup 0.44±0.05}). Thus, the mass-luminosity relation for galaxy groups cannot be described by the same power law as galaxy clusters. A possible explanation for this break is the dynamical friction, tidal interactions, and projection effects that reduce the velocity dispersion values of the galaxy groups. By extending the cluster luminosity function to the group regime, we predict the number of groups that new X-ray surveys, particularly eROSITA, will detect. Based on our

A challenge to dSph formation models: are the most isolated Local Group dSph galaxies truly old?

NASA Astrophysics Data System (ADS)

Monelli, Matteo

2017-08-01

What is the origin of the different dwarf galaxy types? The classification into dwarf irregular (dIrr), spheroidal (dSph), and transition (dT) types is based on their present-day properties. However, star formation histories (SFHs) reconstructed from deep color-magnitude diagrams (CMDs) provide details on the early evolution of galaxies of all these types, and indicate only two basic evolutionary paths. One is characterized by a vigorous but brief initial star-forming event, and little or no star formation thereafter (fast evolution), and the other one by roughly continuous star formation until (nearly) the present time (slow evolution). These two paths do not map directly onto the dIrr, dT and dSph types. Thus, the present galaxy properties do not reflect their lifetime evolution. Since there are some indications that slow dwarfs were assembled in lower-density environments than fast dwarfs, Gallart et al (2015) proposed that the distinction between fast and slow dwarfs reflects the characteristic density of the environment where they formed. This scenario, and more generally scenarios where dSph galaxies formed through the interaction with a massive galaxy, are challenged by a small sample of extremely isolated dSph/dT in the outer fringes of the Local Group. This proposal targets two of these objects (VV124, KKR25) for which we will infer their SFH - through a novel technique that combines the information from their RR Lyrae stars and deep CMDs sampling the intermediate-age population - in order to test these scenarios. This is much less demanding on observing time than classical SFH derivation using full depth CMDs.

Compact configurations within small evolving groups of galaxies

NASA Astrophysics Data System (ADS)

Mamon, G. A.

Small virialized groups of galaxies are evolved with a gravitational N-body code, where the galaxies and a diffuse background are treated as single particles, but with mass and luminosity profiles attached, which enbles the estimation of parameters such as internal energies, half-mass radii, and the softened potential energies of interaction. The numerical treatment includes mergers, collisional stripping, tidal limitation by the mean-field of the background (evaluated using a combination of instantaneous and impulsive formulations), galaxy heating from collisons, and background heating from dynamical friction. The groups start out either as dense as appear the groups in Hickson's (1982) catalog, or as loose as appear those in Turner and Gott's (1976a) catalog, and they are simulated many times (usually 20) with different initial positions and velocities. Dense groups of galaxies with massive dark haloes coalesce into a single galaxy and lose their compact group appearance in approximately 3 group half-mass crossing times, while dense groups of galaxies without massive haloes survive the merger instability for 15 half-mass crossing times (in a more massive background to keep the same total group mass).

Dust-obscured Galaxies in the Local Universe

NASA Astrophysics Data System (ADS)

Hwang, Ho Seong; Geller, Margaret J.

2013-06-01

We use Wide-field Infrared Survey Explorer (WISE), AKARI, and Galaxy Evolution Explorer (GALEX) data to select local analogs of high-redshift (z ~ 2) dust obscured galaxies (DOGs). We identify 47 local DOGs with S 12 μm/S 0.22 μm >= 892 and S 12 μm > 20 mJy at 0.05 < z < 0.08 in the Sloan Digital Sky Survey data release 7. The infrared (IR) luminosities of these DOGs are in the range 3.4 × 1010 (L ⊙) <~ L IR <~ 7.0 × 1011 (L ⊙) with a median L IR of 2.1 × 1011 (L ⊙). We compare the physical properties of local DOGs with a control sample of galaxies that have lower S 12 μm/S 0.22 μm but have similar redshift, IR luminosity, and stellar mass distributions. Both WISE 12 μm and GALEX near-ultraviolet (NUV) flux densities of DOGs differ from the control sample of galaxies, but the difference is much larger in the NUV. Among the 47 DOGs, 36% ± 7% have small axis ratios in the optical (i.e., b/a < 0.6), larger than the fraction among the control sample (17% ± 3%). There is no obvious sign of interaction for many local DOGs. No local DOGs have companions with comparable optical magnitudes closer than ~50 kpc. The large- and small-scale environments of DOGs are similar to the control sample. Many physical properties of local DOGs are similar to those of high-z DOGs, even though the IR luminosities of local objects are an order of magnitude lower than for the high-z objects: the presence of two classes (active galactic nuclei- and star formation-dominated) of DOGs, abnormal faintness in the UV rather than extreme brightness in the mid-IR, and diverse optical morphology. These results suggest a common underlying physical origin of local and high-z DOGs. Both seem to represent the high-end tail of the dust obscuration distribution resulting from various physical mechanisms rather than a unique phase of galaxy evolution.

Dust-obscured galaxies in the local universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hwang, Ho Seong; Geller, Margaret J., E-mail: hhwang@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu

We use Wide-field Infrared Survey Explorer (WISE), AKARI, and Galaxy Evolution Explorer (GALEX) data to select local analogs of high-redshift (z ∼ 2) dust obscured galaxies (DOGs). We identify 47 local DOGs with S {sub 12μm}/S {sub 0.22μm} ≥ 892 and S {sub 12μm} > 20 mJy at 0.05 < z < 0.08 in the Sloan Digital Sky Survey data release 7. The infrared (IR) luminosities of these DOGs are in the range 3.4 × 10{sup 10} (L {sub ☉}) ≲ L {sub IR} ≲ 7.0 × 10{sup 11} (L {sub ☉}) with a median L {sub IR} of 2.1more » × 10{sup 11} (L {sub ☉}). We compare the physical properties of local DOGs with a control sample of galaxies that have lower S {sub 12μm}/S {sub 0.22μm} but have similar redshift, IR luminosity, and stellar mass distributions. Both WISE 12 μm and GALEX near-ultraviolet (NUV) flux densities of DOGs differ from the control sample of galaxies, but the difference is much larger in the NUV. Among the 47 DOGs, 36% ± 7% have small axis ratios in the optical (i.e., b/a < 0.6), larger than the fraction among the control sample (17% ± 3%). There is no obvious sign of interaction for many local DOGs. No local DOGs have companions with comparable optical magnitudes closer than ∼50 kpc. The large- and small-scale environments of DOGs are similar to the control sample. Many physical properties of local DOGs are similar to those of high-z DOGs, even though the IR luminosities of local objects are an order of magnitude lower than for the high-z objects: the presence of two classes (active galactic nuclei- and star formation-dominated) of DOGs, abnormal faintness in the UV rather than extreme brightness in the mid-IR, and diverse optical morphology. These results suggest a common underlying physical origin of local and high-z DOGs. Both seem to represent the high-end tail of the dust obscuration distribution resulting from various physical mechanisms rather than a unique phase of galaxy evolution.« less

THE DEEP2 GALAXY REDSHIFT SURVEY: THE VORONOI-DELAUNAY METHOD CATALOG OF GALAXY GROUPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerke, Brian F.; Newman, Jeffrey A.; Davis, Marc

2012-05-20

We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Galaxy Redshift Survey, including the Extended Groth Strip (EGS). The catalog contains 1165 groups with two or more members in the EGS over the redshift range 0 < z < 1.5 and 1295 groups at z > 0.6 in the rest of DEEP2. Twenty-five percent of EGS galaxies and fourteen percent of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay method (VDM) after it hasmore » been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. In the optimization effort, we have taken particular care to ensure that the mock catalogs resemble the data as closely as possible, and we have fine-tuned our methods separately on mocks constructed for the EGS and the rest of DEEP2. We have also probed the effect of the assumed cosmology on our inferred group-finding efficiency by performing our optimization on three different mock catalogs with different background cosmologies, finding large differences in the group-finding success we can achieve for these different mocks. Using the mock catalog whose background cosmology is most consistent with current data, we estimate that the DEEP2 group catalog is 72% complete and 61% pure (74% and 67% for the EGS) and that the group finder correctly classifies 70% of galaxies that truly belong to groups, with an additional 46% of interloper galaxies contaminating the catalog (66% and 43% for the EGS). We also confirm that the VDM catalog reconstructs the abundance of galaxy groups with velocity dispersions above {approx}300 km s{sup -1} to an accuracy better than the sample variance, and this successful reconstruction is not strongly dependent on cosmology. This makes the DEEP2 group catalog a promising probe of the growth of cosmic structure that can potentially be used for

Galaxy And Mass Assembly (GAMA): the life and times of L★ galaxies

NASA Astrophysics Data System (ADS)

Robotham, A. S. G.; Liske, J.; Driver, S. P.; Sansom, A. E.; Baldry, I. K.; Bauer, A. E.; Bland-Hawthorn, J.; Brough, S.; Brown, M. J. I.; Colless, M.; Christodoulou, L.; Drinkwater, M. J.; Grootes, M. W.; Hopkins, A. M.; Kelvin, L. S.; Norberg, P.; Loveday, J.; Phillipps, S.; Sharp, R.; Taylor, E. N.; Tuffs, R. J.

2013-05-01

In this work, we investigate in detail the effects the local environment (groups and pairs) has on galaxies with stellar mass similar to the Milky Way (L* galaxies). A volume limited sample of 6150 galaxies are visually classified to determine the emission features, morphological type and presence of a disc. This large sample allows for the significant characteristics of galaxies to be isolated (e.g. stellar mass and group halo mass), and their codependencies determined. We observe that galaxy-galaxy interactions play the most important role in shaping the evolution within a group halo; the main role of halo mass is in gathering the galaxies together to encourage such interactions. Dominant pair galaxies find their overall star formation enhanced when the pair's mass ratio is close to 1; otherwise, we observe the same galaxies as we would in an unpaired system. The minor galaxy in a pair is greatly affected by its companion galaxy, and while the star-forming fraction is always suppressed relative to equivalent stellar mass unpaired galaxies, it becomes lower still when the mass ratio of a pair system increases. We find that, in general, the close galaxy-galaxy interaction rate drops as a function of halo mass for a given amount of stellar mass. We find evidence of a local peak of interactions for Milky Way stellar mass galaxies in Milky Way halo mass groups. Low-mass haloes, and in particular Local Group mass haloes, are an important environment for understanding the typical evolutionary path of a unit of stellar mass. We find compelling evidence for galaxy conformity in both groups and pairs, where morphological type conformity is dominant in groups, and emission class conformity is dominant in pairs. This suggests that group scale conformity is the result of many galaxy encounters over an extended period of time, while pair conformity is a fairly instantaneous response to a transitory interaction.

Mapping extragalactic dark matter annihilation with galaxy surveys: A systematic study of stacked group searches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lisanti, Mariangela; Mishra-Sharma, Siddharth; Rodd, Nicholas L.

Dark matter in the halos surrounding galaxy groups and clusters can annihilate to high-energy photons. Recent advancements in the construction of galaxy group catalogs provide many thousands of potential extragalactic targets for dark matter. In this paper, we outline a procedure to infer the dark matter signal associated with a given galaxy group. Applying this procedure to a catalog of sources, one can create a full-sky map of the brightest extragalactic dark matter targets in the nearby Universe (z≲0.03), supplementing sources of dark matter annihilation from within the local group. As with searches for dark matter in dwarf galaxies, thesemore » extragalactic targets can be stacked together to enhance the signals associated with dark matter. We validate this procedure on mock Fermi gamma-ray data sets using a galaxy catalog constructed from the DarkSky N-body cosmological simulation and demonstrate that the limits are robust, at O(1) levels, to systematic uncertainties on halo mass and concentration. We also quantify other sources of systematic uncertainty arising from the analysis and modeling assumptions. Lastly, our results suggest that a stacking analysis using galaxy group catalogs provides a powerful opportunity to discover extragalactic dark matter and complements existing studies of Milky Way dwarf galaxies.« less

Mapping extragalactic dark matter annihilation with galaxy surveys: A systematic study of stacked group searches

NASA Astrophysics Data System (ADS)

Lisanti, Mariangela; Mishra-Sharma, Siddharth; Rodd, Nicholas L.; Safdi, Benjamin R.; Wechsler, Risa H.

2018-03-01

Dark matter in the halos surrounding galaxy groups and clusters can annihilate to high-energy photons. Recent advancements in the construction of galaxy group catalogs provide many thousands of potential extragalactic targets for dark matter. In this paper, we outline a procedure to infer the dark matter signal associated with a given galaxy group. Applying this procedure to a catalog of sources, one can create a full-sky map of the brightest extragalactic dark matter targets in the nearby Universe (z ≲0.03 ), supplementing sources of dark matter annihilation from within the local group. As with searches for dark matter in dwarf galaxies, these extragalactic targets can be stacked together to enhance the signals associated with dark matter. We validate this procedure on mock Fermi gamma-ray data sets using a galaxy catalog constructed from the DarkSky N -body cosmological simulation and demonstrate that the limits are robust, at O (1 ) levels, to systematic uncertainties on halo mass and concentration. We also quantify other sources of systematic uncertainty arising from the analysis and modeling assumptions. Our results suggest that a stacking analysis using galaxy group catalogs provides a powerful opportunity to discover extragalactic dark matter and complements existing studies of Milky Way dwarf galaxies.

Mapping extragalactic dark matter annihilation with galaxy surveys: A systematic study of stacked group searches

DOE PAGES

Lisanti, Mariangela; Mishra-Sharma, Siddharth; Rodd, Nicholas L.; ...

2018-03-09

Dark matter in the halos surrounding galaxy groups and clusters can annihilate to high-energy photons. Recent advancements in the construction of galaxy group catalogs provide many thousands of potential extragalactic targets for dark matter. In this paper, we outline a procedure to infer the dark matter signal associated with a given galaxy group. Applying this procedure to a catalog of sources, one can create a full-sky map of the brightest extragalactic dark matter targets in the nearby Universe (z≲0.03), supplementing sources of dark matter annihilation from within the local group. As with searches for dark matter in dwarf galaxies, thesemore » extragalactic targets can be stacked together to enhance the signals associated with dark matter. We validate this procedure on mock Fermi gamma-ray data sets using a galaxy catalog constructed from the DarkSky N-body cosmological simulation and demonstrate that the limits are robust, at O(1) levels, to systematic uncertainties on halo mass and concentration. We also quantify other sources of systematic uncertainty arising from the analysis and modeling assumptions. Lastly, our results suggest that a stacking analysis using galaxy group catalogs provides a powerful opportunity to discover extragalactic dark matter and complements existing studies of Milky Way dwarf galaxies.« less

The DEEP2 Galaxy Redshift Survey: The Voronoi-Delaunay Method Catalog of Galaxy Groups

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerke, Brian F.; /UC, Berkeley; Newman, Jeffrey A.

2012-02-14

We use the first 25% of the DEEP2 Galaxy Redshift Survey spectroscopic data to identify groups and clusters of galaxies in redshift space. The data set contains 8370 galaxies with confirmed redshifts in the range 0.7 {<=} z {<=} 1.4, over one square degree on the sky. Groups are identified using an algorithm (the Voronoi-Delaunay Method) that has been shown to accurately reproduce the statistics of groups in simulated DEEP2-like samples. We optimize this algorithm for the DEEP2 survey by applying it to realistic mock galaxy catalogs and assessing the results using a stringent set of criteria for measuring group-findingmore » success, which we develop and describe in detail here. We find in particular that the group-finder can successfully identify {approx}78% of real groups and that {approx}79% of the galaxies that are true members of groups can be identified as such. Conversely, we estimate that {approx}55% of the groups we find can be definitively identified with real groups and that {approx}46% of the galaxies we place into groups are interloper field galaxies. Most importantly, we find that it is possible to measure the distribution of groups in redshift and velocity dispersion, n({sigma}, z), to an accuracy limited by cosmic variance, for dispersions greater than 350 km s{sup -1}. We anticipate that such measurements will allow strong constraints to be placed on the equation of state of the dark energy in the future. Finally, we present the first DEEP2 group catalog, which assigns 32% of the galaxies to 899 distinct groups with two or more members, 153 of which have velocity dispersions above 350 km s{sup -1}. We provide locations, redshifts and properties for this high-dispersion subsample. This catalog represents the largest sample to date of spectroscopically detected groups at z {approx} 1.« less

Census of the Local Universe (CLU) Hα Galaxy Survey: Characterization of Galaxy Catalogs from Preliminary Fields

NASA Astrophysics Data System (ADS)

Cook, David O.; Kasliwal, Mansi; Van Sistine, Anglea; Kaplan, David; iPTF

2018-01-01

In this talk I introduce the Census of the Local Universe (CLU) galaxy survey. The survey uses 4 wavelength-adjacent, narrowband filters to search for emission-line (Hα) sources across ~3π (26,470 deg2) of the sky and out to distance of 200 Mpc. I will present an analysis of galaxy candidates in 14 preliminary fields (out of 3626) to assess the limits of the survey and the potential for finding new galaxies in the local Universe. We anticipate finding tens-of-thousands of new galaxies in the full ~3π survey. In addition, I present some interesting galaxies found in these fields, which include: newly discovered blue compact dwarfs (e.g., blueberries), 1 new green pea, 1 new QSO, and a known planetary nebula. The majority of the CLU galaxies show properties similar to normal star-forming galaxies; however, the newly discovered blueberries tend to have high star formation rates for their given stellar mass.

The Effect of Halo Mass on the H I Content of Galaxies in Groups and Clusters

NASA Astrophysics Data System (ADS)

Yoon, Ilsang; Rosenberg, Jessica L.

2015-10-01

We combine data from the Sloan Digital Sky Survey (SDSS) and the Arecibo Legacy Fast ALFA Survey (ALFALFA) to study the cold atomic gas content of galaxies in groups and clusters in the local universe. A careful cross-matching of galaxies in the SDSS, ALFALFA, and SDSS group catalogs provides a sample of group galaxies with stellar masses {10}8.4{M}⊙ ≤slant {M}*≤slant {10}10.6{M}⊙ and group halo masses {10}12.5{h}-1{M}⊙ ≤slant {M}h≤slant {10}15.0{h}-1{M}⊙ . Controlling our sample in stellar mass and redshift, we find no significant radial variation in the galaxy H i gas-to-stellar mass ratio for the halo mass range in our sample. However, the fraction of galaxies detected in ALFALFA declines steadily toward the centers of groups, with the effect being most prominent in the most massive halos. In the outskirts of massive halos a hint of a depressed detection fraction for low-mass galaxies suggests pre-processing that decreases the H i in these galaxies before they fall into massive clusters. We interpret the decline in the ALFALFA detection of galaxies in the context of a threshold halo mass for ram pressure stripping for a given galaxy stellar mass. The lack of an observable decrease in the galaxy H i gas-to-stellar mass ratio with the position of galaxies within groups and clusters highlights the difficulty of detecting the impact of environment on the galaxy H i content in a shallow H i survey.

Integrated HI emission in galaxy groups and clusters

NASA Astrophysics Data System (ADS)

Ai, Mei; Zhu, Ming; Fu, Jian

2017-09-01

The integrated HI emission from hierarchical structures such as groups and clusters of galaxies can be detected by FAST at intermediate redshifts. Here we propose to use FAST to study the evolution of the global HI content of clusters and groups over cosmic time by measuring their integrated HI emissions. We use the Virgo Cluster as an example to estimate the detection limit of FAST, and have estimated the integration time to detect a Virgo type cluster at different redshifts (from z = 0.1 to z = 1.5).We have also employed a semi-analytic model (SAM) to simulate the evolution of HI contents in galaxy clusters. Our simulations suggest that the HI mass of a Virgo-like cluster could be 2-3 times higher and the physical size could be more than 50% smaller when redshift increases from z = 0.3 to z = 1. Thus the integration time could be reduced significantly and gas rich clusters at intermediate redshifts can be detected by FAST in less than 2 hours of integration time. For the local Universe, we have also used SAM simulations to create mock catalogs of clusters to predict the outcomes from FAST all sky surveys. Comparing with the optically selected catalogs derived by cross matching the galaxy catalogs from the SDSS survey and the ALFALFA survey, we find that the HI mass distribution of the mock catalog with 20 s of integration time agrees well with that of observations. However, the mock catalog with 120 s of integration time predicts many more groups and clusters that contain a population of low mass HI galaxies not detected by the ALFALFA survey. A future deep HI blind sky survey with FAST would be able to test such prediction and set constraints on the numerical simulation models. The observational strategy and sample selections for future FAST observations of galaxy clusters at high redshifts are also discussed.

Metallicities of Galaxies in the Local Universe

NASA Astrophysics Data System (ADS)

Hirschauer, Alec Seth

2018-01-01

The degree of heavy-element enrichment for star-forming galaxies in the universe is a fundamental astrophysical characteristic which traces the amount of stellar nucleosynthesis undertaken by the constituent population of stars. Estimating this quantity via the so-called "direct-method" is observationally challenging and requires measurement of intrinsically weak temperature-sensitive nebular emission lines, however these are typically not found for galaxies unless their emission lines are exceptionally bright. Metal abundances ("metallicities") must then therefore be estimated by empirical means utilizing ratios of strong emission lines, calibrated to sources of known abundance and/or theoretical models, which are measurable in essentially any nebular spectrum of a star-forming system. Relationships concerning metallicities in galaxies such as the luminosity-metallicity and mass-metallicity are critically dependent upon reliable estimations of abundances. Therefore, having a reliable observational constraint is paramount to developing models which accurately reflect the universe. This dissertation presentation explores metallicities for galaxies in the local universe through a variety of means. First, an attempt is made to improve calibrations of empirical relationships for estimating abundances for star-forming galaxies at high-metallicities, finding some intrinsic shortcomings but also revealing some interesting new findings regarding the computation of the electron gas of star-forming systems, as well as detecting some anomalously under-abundant, overly-luminous galaxies. Second, the development of a self-consistent scale for estimating metallicities allows for the creation of luminosity-metallicity and mass-metallicity relations for a statistically representative sample of star-forming galaxies in the local universe. Finally, a discovery is made of an extremely metal-poor star-forming galaxy, which opens the possibility to find more similar systems and to

Galaxy interactions in the Hickson Compact Group 88

NASA Astrophysics Data System (ADS)

Brosch, Noah

2015-12-01

I present observations of the Hickson Compact Group 88 (HCG88) obtained during the commissioning of a new 28-inch telescope at the Wise Observatory. This galaxy group was advertized to be non-interacting, or to be in a very early interaction stage, but this is not the case. The observations reported here were done using a `luminance' filter, essentially a very broad R filter, reaching a low surface brightness level of ≈26 mag arcsec-2. Additional observations were obtained in a narrow spectral band approximately centred on the rest-frame H α line from the group. Contrary to previous studies, my observations show that at least two of the major galaxies have had significant interactions in the past, although probably not between themselves. I report the discovery of a faint extended tail emerging from the brightest of the group galaxies, severe isophote twisting and possible outer shells around another galaxy, and map the H II regions in all the galaxies.

Exploring X-Ray Binary Populations in Compact Group Galaxies With Chandra

NASA Technical Reports Server (NTRS)

Tzanavaris, P.; Hornschemeier, A. E..; Gallagher, S. C.; Lenkic, L.; Desjardins, T. D.; Walker, L. M.; Johnson, K. E.; Mulchaey, J. S.

2016-01-01

We obtain total galaxy X-ray luminosities, LX, originating from individually detected point sources in a sample of 47 galaxies in 15 compact groups of galaxies (CGs). For the great majority of our galaxies, we find that the detected point sources most likely are local to their associated galaxy, and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic nuclei (AGNs). For spiral and irregular galaxies, we find that, after accounting for AGNs and nuclear sources, most CG galaxies are either within the +/-1s scatter of the Mineo et al. LX-star formation rate (SFR) correlation or have higher LX than predicted by this correlation for their SFR. We discuss how these "excesses" may be due to low metallicities and high interaction levels. For elliptical and S0 galaxies, after accounting for AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et al. LX-stellar mass correlation for low-mass XRBs, with larger scatter, likely due to residual effects such as AGN activity or hot gas. Assuming non-nuclear sources are low- or high-mass XRBs, we use appropriate XRB luminosity functions to estimate the probability that stochastic effects can lead to such extreme LX values. We find that, although stochastic effects do not in general appear to be important, for some galaxies there is a significant probability that high LX values can be observed due to strong XRB variability.

Nebular Metallicities in Two Isolated Local Void Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Nicholls, David C.; Jerjen, Helmut; Dopita, Michael A.; Basurah, Hassan

2014-01-01

Isolated dwarf galaxies, especially those situated in voids, may provide insight into primordial conditions in the universe and the physical processes that govern star formation in undisturbed stellar systems. The metallicity of H II regions in such galaxies is key to investigating this possibility. From the SIGRID sample of isolated dwarf galaxies, we have identified two exceptionally isolated objects, the Local Void galaxy [KK98]246 (ESO 461-G036) and another somewhat larger dwarf irregular on the edge of the Local Void, MCG-01-41-006 (HIPASS J1609-04). We report our measurements of the nebular metallicities in these objects. The first object has a single low luminosity H II region, while the second is in a more vigorous star forming phase with several bright H II regions. We find that the metallicities in both galaxies are typical for galaxies of this size, and do not indicate the presence of any primordial gas, despite (for [KK98]246) the known surrounding large reservoir of neutral hydrogen.

The red-sequence of 72 WINGS local galaxy clusters

NASA Astrophysics Data System (ADS)

Valentinuzzi, T.; Poggianti, B. M.; Fasano, G.; D'Onofrio, M.; Moretti, A.; Ramella, M.; Biviano, A.; Fritz, J.; Varela, J.; Bettoni, D.; Vulcani, B.; Moles, M.; Couch, W. J.; Dressler, A.; Kjærgaard, P.; Omizzolo, A.; Cava, A.

2011-12-01

We study the color - magnitude red sequence and blue fraction of 72 X-ray selected galaxy clusters at z = 0.04-0.07 from the WINGS survey, searching for correlations between the characteristics of the red sequence (RS) and the environment. We consider the slope and scatter of the red sequence, the number ratio of red luminous-to-faint galaxies, the blue fraction, and the fractions of ellipticals, S0s, and spirals that compose the RS. None of these quantities correlate with the cluster velocity dispersion, X-ray luminosity, number of cluster substructures, BCG prevalence over next brightest galaxies, and the spatial concentration of ellipticals. The properties of the RS, instead, depend strongly on local galaxy density. Higher density regions have a smaller RS scatter, a higher luminous-to-faint ratio, a lower blue fraction, and a lower spiral fraction on the RS. Our results clearly illustrate the prominent effect of the local density in setting the epoch when galaxies become passive and join the red sequence, as opposed to the mass of the galaxy host structure.

Clusters of Galaxies

NASA Astrophysics Data System (ADS)

Huchtmeier, W. K.; Richter, O. G.; Materne, J.

1981-09-01

The large-scale structure of the universe is dominated by clustering. Most galaxies seem to be members of pairs, groups, clusters, and superclusters. To that degree we are able to recognize a hierarchical structure of the universe. Our local group of galaxies (LG) is centred on two large spiral galaxies: the Andromeda nebula and our own galaxy. Three sr:naller galaxies - like M 33 - and at least 23 dwarf galaxies (KraanKorteweg and Tammann, 1979, Astronomische Nachrichten, 300, 181) can be found in the evironment of these two large galaxies. Neighbouring groups have comparable sizes (about 1 Mpc in extent) and comparable numbers of bright members. Small dwarf galaxies cannot at present be observed at great distances.

On the Formation of Elliptical Galaxies via Mergers in Galaxy Groups

NASA Astrophysics Data System (ADS)

Taranu, Dan; Dubinski, John; Yee, Howard K. C.

2015-08-01

Giant elliptical galaxies have long been thought to form through gas-rich "major" mergers of two roughly equal-mass spiral galaxies. However, ellipticals are often found at the centers of groups and are likely to have undergone several significant mergers since z=2. We test the hypothesis that ellipticals form through multiple, mainly minor and dry mergers in groups, using hundreds of N-body simulations of mergers in groups of three to twenty-five spirals (Taranu et al. 2013).Realistic mock observations of the central merger remnants show that they have similar surface brightness profiles to local ellipticals. The size-luminosity and velocity dispersion-luminosity relations have modest (~0.1 dex) scatter, with similar slopes; however, most remnants are too large and have too low dispersions for their luminosities. Some remnants show substantial (v/σ > 0.1) rotational support, but most are slow rotators with v/σ << 0.5.Ellipticals also follow a tight "fundamental plane" scaling relation between size R, mean surface brightness μ and velocity dispersion σ: R ∝ σ^a μ^b. This relation has small (<0.06 dex) scatter and significantly different coefficients from the expected scaling (a "tilt"). The remnants lie on a similar fundamental plane, with even smaller scatter (0.02 dex) and a tilt in the correct sense - albeit weaker than observed. This tilt is caused by variable dark matter fractions within the effective radius, such that massive merger remnants have larger central dark matter fractions than their lower-mass counterparts (Taranu et al. 2015).These results suggest that massive ellipticals can originate from multiple, mainly minor and dry mergers of spirals at z<2, producing tight scaling relations in the process. However, significant gas dissipation and/or more compact progenitor spirals may be needed to produce lower-mass, rapidly-rotating ellipticals. I will also show preliminary results from simulations with more realistic progenitor galaxies (including

Morphology and luminosity segregation of galaxies in nearby loose groups

NASA Astrophysics Data System (ADS)

Girardi, M.; Rigoni, E.; Mardirossian, F.; Mezzetti, M.

2003-08-01

We study morphology and luminosity segregation of galaxies in loose groups. We analyze the two catalogs of groups identified in the Nearby Optical Galaxy (NOG) sample, by means of hierarchical and percolation ``friends-of-friends'' methods (HG and PG catalogs, respectively). In the first part of our analysis we consider 387 and 436 groups of HG and PG and compare morphology- (luminosity-) weighted to unweighted group properties: velocity dispersion, mean pairwise distance, and mean groupcentric distance of member galaxies. The second part of our analysis is based on two ensemble systems, one for each catalog, built by suitably combining together galaxies of all groups (1584 and 1882 galaxies for HG and PG groups). We find that earlier-type (brighter) galaxies are more clustered and lie closer to the group centers, both in position and in velocity, than later-type (fainter) galaxies. Spatial segregations are stronger than kinematical segregations. These effects are generally detected at the >˜ 3-sigma level. Luminosity segregation is shown to be independent of morphology segregation. Our main conclusions are strengthened by the detection of segregation in both hierarchical and percolation catalogs. Our results agree with a continuum of segregation properties of galaxies in systems, from low-mass groups to massive clusters.

Examining the Center: Positions, Dominance, and Star Formation Rates of Most Massive Group Galaxies at Intermediate Redshift

NASA Astrophysics Data System (ADS)

Connelly, Jennifer L.; Parker, Laura C.; McGee, Sean; Mulchaey, John S.; Finoguenov, Alexis; Balogh, Michael; Wilman, David; Group Environment Evolution Collaboration

2015-01-01

The group environment is believed to be the stage for many galaxy transformations, helping evolve blue star-forming galaxies to red passive ones. In local studies of galaxy clusters, the central member is usually a single dominant giant galaxy at the center of the potential with little star formation thought to be the result of galaxy mergers. In nearby groups, a range of morphologies and star formation rates are observed and the formation history is less clear. Further, the position and dominance of the central galaxy cannot be assumed in groups, which are less massive and evolved than clusters. To understand the connections between global group properties and properties of the central group galaxy at intermediate redshift, we examine galaxy groups from the Group Environment and Evolution Collaboration (GEEC) catalog, including both optically- and X-ray-selected groups at redshift z~0.4. The sample is diverse, containing a range in overall mass and evolutionary state. The number of groups is significant, membership is notably complete, and measurements span the IR to the UV allowing the properties of the members to be connected to those of the host groups. Having investigated trends in the global group properties previously, including mass and velocity substructure, we turn our attention now to the galaxy populations, focusing on the central regions of these systems. The most massive and second most massive group galaxies are identified by their stellar mass. The positions of the most massive galaxies (MMGs) are determined with respect to both the luminosity-weighted and X-ray center. Star formation rates are used to explore the fraction of passive/quiescent versus star-forming MMGs and the dominance of the MMGs in our group sample is also tested. Determinations of these characteristics and trends constitute the important first steps toward a detailed understanding of the relationships between the properties of host groups and their most massive galaxies and the

Dark matter searches with Cherenkov telescopes: nearby dwarf galaxies or local galaxy clusters?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sánchez-Conde, Miguel A.; Cannoni, Mirco; Gómez, Mario E.

2011-12-01

In this paper, we compare dwarf galaxies and galaxy clusters in order to elucidate which object class is the best target for gamma-ray DM searches with imaging atmospheric Cherenkov telescopes (IACTs). We have built a mixed dwarfs+clusters sample containing some of the most promising nearby dwarf galaxies (Draco, Ursa Minor, Wilman 1 and Segue 1) and local galaxy clusters (Perseus, Coma, Ophiuchus, Virgo, Fornax, NGC 5813 and NGC 5846), and then compute their DM annihilation flux profiles by making use of the latest modeling of their DM density profiles. We also include in our calculations the effect of DM substructure.more » Willman 1 appears as the best candidate in the sample. However, its mass modeling is still rather uncertain, so probably other candidates with less uncertainties and quite similar fluxes, namely Ursa Minor and Segue 1, might be better options. As for galaxy clusters, Virgo represents the one with the highest flux. However, its large spatial extension can be a serious handicap for IACT observations and posterior data analysis. Yet, other local galaxy cluster candidates with more moderate emission regions, such as Perseus, may represent good alternatives. After comparing dwarfs and clusters, we found that the former exhibit annihilation flux profiles that, at the center, are roughly one order of magnitude higher than those of clusters, although galaxy clusters can yield similar, or even higher, integrated fluxes for the whole object once substructure is taken into account. Even when any of these objects are strictly point-like according to the properties of their annihilation signals, we conclude that dwarf galaxies are best suited for observational strategies based on the search of point-like sources, while galaxy clusters represent best targets for analyses that can deal with rather extended emissions. Finally, we study the detection prospects for present and future IACTs in the framework of the constrained minimal supersymmetric standard

Dark Matter Searches with Cherenkov Telescopes: Nearby Dwarf Galaxies or Local Galaxy Clusters?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanchez-Conde, Miguel A.; /KIPAC, Menlo Park /SLAC /IAC, La Laguna /Laguna U., Tenerife; Cannoni, Mirco

2012-06-06

In this paper, we compare dwarf galaxies and galaxy clusters in order to elucidate which object class is the best target for gamma-ray DM searches with imaging atmospheric Cherenkov telescopes (IACTs). We have built a mixed dwarfs+clusters sample containing some of the most promising nearby dwarf galaxies (Draco, Ursa Minor, Wilman 1 and Segue 1) and local galaxy clusters (Perseus, Coma, Ophiuchus, Virgo, Fornax, NGC 5813 and NGC 5846), and then compute their DM annihilation flux profiles by making use of the latest modeling of their DM density profiles. We also include in our calculations the effect of DM substructure.more » Willman 1 appears as the best candidate in the sample. However, its mass modeling is still rather uncertain, so probably other candidates with less uncertainties and quite similar fluxes, namely Ursa Minor and Segue 1, might be better options. As for galaxy clusters, Virgo represents the one with the highest flux. However, its large spatial extension can be a serious handicap for IACT observations and posterior data analysis. Yet, other local galaxy cluster candidates with more moderate emission regions, such as Perseus, may represent good alternatives. After comparing dwarfs and clusters, we found that the former exhibit annihilation flux profiles that, at the center, are roughly one order of magnitude higher than those of clusters, although galaxy clusters can yield similar, or even higher, integrated fluxes for the whole object once substructure is taken into account. Even when any of these objects are strictly point-like according to the properties of their annihilation signals, we conclude that dwarf galaxies are best suited for observational strategies based on the search of point-like sources, while galaxy clusters represent best targets for analyses that can deal with rather extended emissions. Finally, we study the detection prospects for present and future IACTs in the framework of the constrained minimal supersymmetric standard

Dark matter searches with Cherenkov telescopes: nearby dwarf galaxies or local galaxy clusters?

NASA Astrophysics Data System (ADS)

Sánchez-Conde, Miguel A.; Cannoni, Mirco; Zandanel, Fabio; Gómez, Mario E.; Prada, Francisco

2011-12-01

In this paper, we compare dwarf galaxies and galaxy clusters in order to elucidate which object class is the best target for gamma-ray DM searches with imaging atmospheric Cherenkov telescopes (IACTs). We have built a mixed dwarfs+clusters sample containing some of the most promising nearby dwarf galaxies (Draco, Ursa Minor, Wilman 1 and Segue 1) and local galaxy clusters (Perseus, Coma, Ophiuchus, Virgo, Fornax, NGC 5813 and NGC 5846), and then compute their DM annihilation flux profiles by making use of the latest modeling of their DM density profiles. We also include in our calculations the effect of DM substructure. Willman 1 appears as the best candidate in the sample. However, its mass modeling is still rather uncertain, so probably other candidates with less uncertainties and quite similar fluxes, namely Ursa Minor and Segue 1, might be better options. As for galaxy clusters, Virgo represents the one with the highest flux. However, its large spatial extension can be a serious handicap for IACT observations and posterior data analysis. Yet, other local galaxy cluster candidates with more moderate emission regions, such as Perseus, may represent good alternatives. After comparing dwarfs and clusters, we found that the former exhibit annihilation flux profiles that, at the center, are roughly one order of magnitude higher than those of clusters, although galaxy clusters can yield similar, or even higher, integrated fluxes for the whole object once substructure is taken into account. Even when any of these objects are strictly point-like according to the properties of their annihilation signals, we conclude that dwarf galaxies are best suited for observational strategies based on the search of point-like sources, while galaxy clusters represent best targets for analyses that can deal with rather extended emissions. Finally, we study the detection prospects for present and future IACTs in the framework of the constrained minimal supersymmetric standard model. We

Are groups of galaxies virialized systems?

NASA Technical Reports Server (NTRS)

Diaferio, Antonaldo; Ramella, Massimo; Geller, Margaret J.; Ferrari, Attilio

1993-01-01

Groups are systems of galaxies with crossing times t(cr) much smaller than the Hubble time. Most of them have t(cr) less than 0.1/H0. The usual interpretation is that they are in virial equilibrium. We compare the data of the group catalog selected from the CfA redshift survey extension with different N-body models. We show that the distributions of kinematic and dynamical quantities of the groups in the CfA catalog can be reproduced by a single collapsing group observed along different line of sights. This result shows that (1) projection effects dominate the statistics of these systems, and (2) observed groups of galaxies are probably still in the collapse phase.

A study of star formation by Hα emission of galaxies in the galaxy group NGC 4213

NASA Astrophysics Data System (ADS)

Maungkorn, Sakdawoot; Kriwattanawong, Wichean

2017-09-01

This research aims to study hydrogen alpha emission, corresponding to star formation of galaxies in the NGC 4213 group that has an average recession velocity of 6,821 km/s. The imaging observations with broad-band filters (B, V and RC) and narrow-band filters ([S II] and Red-continuum) were carried out from the 2.4-m reflecting telescope at Thai National Observatory (TNO). There are 11 sample galaxies in this study, consisting of 2 elliptical, 2 lenticular and 7 spiral galaxies. It was found that the late-type galaxies tend to be bluer than early-type galaxies, due to these galaxies consist of relatively high proportion of blue stars. Furthermore, the equivalent width of hydrogen alpha (EW(Hα)) tends to increase as a function of morphological type. This indicates that star formation in late-type galaxies taking place more than the early-type galaxies. Furthermore, a ratio of the star formation rate to galaxy mass also increases slightly with the galaxy type. This could be due to the interaction between galaxy-galaxy or tidal interaction occurring within the galaxy group.

SPECTROSCOPIC CONFIRMATION OF THE DWARF SPHEROIDAL GALAXY d0994+71 AS A MEMBER OF THE M81 GROUP OF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Toloba, Elisa; Sand, David; Crnojević, Denija

2016-10-10

We use Keck/DEIMOS spectroscopy to measure the first velocity and metallicity of a dwarf spheroidal (dSph) galaxy beyond the Local Group using resolved stars. Our target, d0944+71, is a faint dSph found in the halo of the massive spiral galaxy M81 by Chiboucas et al. We coadd the spectra of 27 individual stars and measure a heliocentric radial velocity of −38 ± 10 km s{sup −1}. This velocity is consistent with d0944+71 being gravitationally bound to M81. We coadd the spectra of the 23 stars that are consistent with being red giant branch stars and measure an overall metallicity ofmore » [Fe/H] = −1.3 ± 0.3 based on the calcium triplet lines. This metallicity is consistent with d0944+71 following the metallicity−luminosity relation for Local Group dSphs. We investigate several potential sources of observational bias but find that our sample of targeted stars is representative of the metallicity distribution function of d0944+71 and any stellar contamination due to seeing effects is negligible. The low ellipticity of the galaxy and its position in the metallicity−luminosity relation suggest that d0944+71 has not been affected by strong tidal stripping.« less

The shell galaxy NGC4104 in an X-ray group

NASA Astrophysics Data System (ADS)

Lima Neto, G. B.; Durret, F.; Laganá, T.; Machado, R. E. G.; Martinet, N.

2017-07-01

Groups of galaxies are expected to collapse early in the history of the universe, in particular the so-called Fossil Groups, with a central galaxy that grows at the bottom of the gravitational potential well by cannibalizing smaller galaxies and/or by major mergers. An evidence of galactic cannibalism is the feature known as shells or ripples in early-type galaxies Shell galaxies are believed to be the result of a minor merger of a dwarf with an elliptical galaxy, resulting in a series of faint concentric ripples in surface brightness observed throughout the main stellar component. This contribution presents very deep r and g imaging of NGC 4104 - the brightest galaxy of an X-ray emitting group - obtained with MegaCam on the 3.6 m CFHT. Using both iraf/ellipse and galfit 2D image-fitting programs, we show the presence of strong shell features and an extended stellar halo around the group brightest galaxy. We have run a series of N-body simulations in order to gain insight on the dynamical process that shaped NGC 4104. Numerical modeling suggests a recent (around 5 Gyrs ago) collision occurred with a dwarf galaxy, which may have also led to a central absorption feature observed in the galaxy center. Moreover, given the magnitude gap between the first and second brightest galaxies, it seems that we are witnessing the formation of an object that falls within the fossil group classification.

A CATALOG OF ULTRA-COMPACT HIGH VELOCITY CLOUDS FROM THE ALFALFA SURVEY: LOCAL GROUP GALAXY CANDIDATES?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P., E-mail: betsey@astro.cornell.edu, E-mail: riccardo@astro.cornell.edu, E-mail: haynes@astro.cornell.edu

2013-05-01

We present a catalog of 59 ultra-compact high velocity clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34 Jy km s{sup -1}, median angular diameters of 10', and median velocity widths of 23 km s{sup -1}. We show that the full UCHVC population cannot easily be associated with known populations of high velocity clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distributionmore » and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of {approx}1 Mpc, the UCHVCs have neutral hydrogen (H I) masses of {approx}10{sup 5}-10{sup 6} M{sub Sun }, H I diameters of {approx}2-3 kpc, and indicative dynamical masses within the H I extent of {approx}10{sup 7}-10{sup 8} M{sub Sun }, similar to the Local Group ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.« less

Stellar Populations in the Local Group: Contribution from Planetary Nebulae

NASA Astrophysics Data System (ADS)

Maciel, W. J.; Costa, R. D. D.; Idiart, T. E. P.; Escudero, A. V.

2007-05-01

The role of planetary nebulae (PN) as a key indicator of stellar populations both in the Milky Way and in galaxies of the Local Group has been emphasized in some recent publications (see for example Maciel et al. 2006, Planetary nebulae beyond the Milky Way, ed. L. Stanghellini, J.R. Walsh, N. G. Douglas, Springer, p.209; Richer and McCall 2006, ibid, p. 220; Buzzoni et al. 2006, MNRAS (in press); Ciardullo, R. 2006, IAU Symposium 234, ed. M.J. Barlow, R.H. Mendez, ASP, in press). As the offspring of stars within a reasonably large mass bracket (0.8 to about 8 solar masses), PN encompass an equally large age spread, as well as different spatial and kinematic distributions. For example, in spiral galaxies PN have different properties depending on their location in the disk, bulge or halo populations. They usually present bright emission lines and can be easily distinguished from other emission line objects, so that their chemical composition and spatiokinematical properties are relatively well determined. Therefore, they are particularly suitable for stellar population studies. In this work, we take into account the available data samples of PN in Local Group galaxies and compare the derived information from different objects, particularly regarding the luminosity-specific PN number density, the chemical composition, space distribution and kinematics. Data by our own group on the Milky Way and Magellanic Clouds are combined with recent surveys and theoretical analyses of other galaxies in the Local Group. Special emphasis is given to the disk and bulge populations of PN in the Milky Way and M31, including an analysis of the metallicity distribution, presence of abundance gradients and a determination of the luminosity function from planetary nebulae.

Galaxy And Mass Assembly (GAMA): the effect of galaxy group environment on active galactic nuclei

NASA Astrophysics Data System (ADS)

Gordon, Yjan A.; Pimbblet, Kevin A.; Owers, Matt S.; Bland-Hawthorn, Joss; Brough, Sarah; Brown, Michael J. I.; Cluver, Michelle E.; Croom, Scott M.; Holwerda, Benne W.; Loveday, Jonathan; Mahajan, Smriti; Wang, Lingyu

2018-04-01

In galaxy clusters, efficiently accreting active galactic nuclei (AGNs) are preferentially located in the infall regions of the cluster projected phase-space, and are rarely found in the cluster core. This has been attributed to both an increase in triggering opportunities for infalling galaxies, and a reduction of those mechanisms in the hot, virialized, cluster core. Exploiting the depth and completeness (98 per cent at r < 19.8 mag) of the Galaxy And Mass Assembly survey (GAMA), we probe down the group halo mass function to assess whether AGNs are found in the same regions in groups as they are in clusters. We select 451 optical AGNs from 7498 galaxies with log10(M*/M⊙) > 9.9 in 695 groups with 11.53 ≤ log10(M200/M⊙) ≤ 14.56 at z < 0.15. By analysing the projected phase-space positions of these galaxies, we demonstrate that when split both radially, and into physically derived infalling and core populations, AGN position within group projected phase-space is dependent on halo mass. For groups with log10(M200/M⊙) > 13.5, AGNs are preferentially found in the infalling galaxy population with 3.6σ confidence. At lower halo masses, we observe no difference in AGN fraction between core and infalling galaxies. These observations support a model where a reduced number of low-speed interactions, ram pressure stripping and intra-group/cluster medium temperature, the dominance of which increase with halo mass, work to inhibit AGN in the cores of groups and clusters with log10(M200/M⊙) > 13.5, but do not significantly affect nuclear activity in cores of less massive structures.

MID-INFRARED EVIDENCE FOR ACCELERATED EVOLUTION IN COMPACT GROUP GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walker, Lisa May; Johnson, Kelsey E.; Gallagher, Sarah C.

2010-11-15

Compact galaxy groups are at the extremes of the group environment, with high number densities and low velocity dispersions that likely affect member galaxy evolution. To explore the impact of this environment in detail, we examine the distribution in the mid-infrared (MIR) 3.6-8.0 {mu}m color space of 42 galaxies from 12 Hickson compact groups (HCGs) in comparison with several control samples, including the LVL+SINGS galaxies, interacting galaxies, and galaxies from the Coma Cluster. We find that the HCG galaxies are strongly bimodal, with statistically significant evidence for a gap in their distribution. In contrast, none of the other samples showmore » such a marked gap, and only galaxies in the Coma infall region have a distribution that is statistically consistent with the HCGs in this parameter space. To further investigate the cause of the HCG gap, we compare the galaxy morphologies of the HCG and LVL+SINGS galaxies, and also probe the specific star formation rate (SSFR) of the HCG galaxies. While galaxy morphology in HCG galaxies is strongly linked to position with MIR color space, the more fundamental property appears to be the SSFR, or star formation rate normalized by stellar mass. We conclude that the unusual MIR color distribution of HCG galaxies is a direct product of their environment, which is most similar to that of the Coma infall region. In both cases, galaxy densities are high, but gas has not been fully processed or stripped. We speculate that the compact group environment fosters accelerated evolution of galaxies from star-forming and neutral gas-rich to quiescent and neutral gas-poor, leaving few members in the MIR gap at any time.« less

The Complete Local-Volume Groups Sample (CLoGS): Early results from X-ray and radio observations

NASA Astrophysics Data System (ADS)

Vrtilek, Jan M.; O'Sullivan, Ewan; David, Laurence P.; Giacintucci, Simona; Kolokythas, Konstantinos

2017-08-01

Although the group environment is the dominant locus of galaxy evolution (in contrast to rich clusters, which contain only a few percent of galaxies), there has been a lack of reliable, representative group samples in the local Universe. In particular, X-ray selected samples are strongly biased in favor of the X-ray bright, centrally-concentrated cool-core systems. In response, we have designed the Complete Local-Volume Groups Sample (CLoGS), an optically-selected statistically-complete sample of 53 groups within 80 Mpc which is intended to overcome the limitations of X-ray selected samples and serve as a representative survey of groups in the local Universe. We have supplemented X-ray data from Chandra and XMM (70% complete to date, using both archival and new observations, with a 26-group high richness subsample 100% complete) with GMRT radio continuum observations (at 235 and 610 MHz, complete for the entire sample). CLoGS includes groups with a wide variety of properties in terms of galaxy population, hot gas content, and AGN power. We here describe early results from the survey, including the range of AGN activity observed in the dominant galaxies, the relative fraction of cool-core and non-cool-core groups in our sample, and the degree of disturbance observed in the IGM.

The Large Local Hole in the Galaxy Distribution: The 2MASS Galaxy Angular Power Spectrum

NASA Astrophysics Data System (ADS)

Frith, W. J.; Outram, P. J.; Shanks, T.

2005-06-01

We present new evidence for a large deficiency in the local galaxy distribution situated in the ˜4000 deg2 APM survey area. We use models guided by the 2dF Galaxy Redshift Survey (2dFGRS) n(z) as a probe of the underlying large-scale structure. We first check the usefulness of this technique by comparing the 2dFGRS n(z) model prediction with the K-band and B-band number counts extracted from the 2MASS and 2dFGRS parent catalogues over the 2dFGRS Northern and Southern declination strips, before turning to a comparison with the APM counts. We find that the APM counts in both the B and K-bands indicate a deficiency in the local galaxy distribution of ˜30% to z ≈ 0.1 over the entire APM survey area. We examine the implied significance of such a large local hole, considering several possible forms for the real-space correlation function. We find that such a deficiency in the APM survey area indicates an excess of power at large scales over what is expected from the correlation function observed in 2dFGRS correlation function or predicted from ΛCDM Hubble Volume mock catalogues. In order to check further the clustering at large scales in the 2MASS data, we have calculated the angular power spectrum for 2MASS galaxies. Although in the linear regime (l<30), ΛCDM models can give a good fit to the 2MASS angular power spectrum, over a wider range (l<100) the power spectrum from Hubble Volume mock catalogues suggests that scale-dependent bias may be needed for ΛCDM to fit. However, the modest increase in large-scale power observed in the 2MASS angular power spectrum is still not enough to explain the local hole. If the APM survey area really is 25% deficient in galaxies out to z≈0.1, explanations for the disagreement with observed galaxy clustering statistics include the possibilities that the galaxy clustering is non-Gaussian on large scales or that the 2MASS volume is still too small to represent a `fair sample' of the Universe. Extending the 2dFGRS redshift survey

A Bridge from Optical to Infrared Galaxies: Explaining Local Properties and Predicting Galaxy Counts and the Cosmic Background Radiation

NASA Astrophysics Data System (ADS)

Totani, Tomonori; Takeuchi, Tsutomu T.

2002-05-01

We give an explanation for the origin of various properties observed in local infrared galaxies and make predictions for galaxy counts and cosmic background radiation (CBR) using a new model extended from that for optical/near-infrared galaxies. Important new characteristics of this study are that (1) mass scale dependence of dust extinction is introduced based on the size-luminosity relation of optical galaxies and that (2) the large-grain dust temperature Tdust is calculated based on a physical consideration for energy balance rather than by using the empirical relation between Tdust and total infrared luminosity LIR found in local galaxies, which has been employed in most previous works. Consequently, the local properties of infrared galaxies, i.e., optical/infrared luminosity ratios, LIR-Tdust correlation, and infrared luminosity function are outputs predicted by the model, while these have been inputs in a number of previous models. Our model indeed reproduces these local properties reasonably well. Then we make predictions for faint infrared counts (in 15, 60, 90, 170, 450, and 850 μm) and CBR using this model. We found results considerably different from those of most previous works based on the empirical LIR-Tdust relation; especially, it is shown that the dust temperature of starbursting primordial elliptical galaxies is expected to be very high (40-80 K), as often seen in starburst galaxies or ultraluminous infrared galaxies in the local and high-z universe. This indicates that intense starbursts of forming elliptical galaxies should have occurred at z~2-3, in contrast to the previous results that significant starbursts beyond z~1 tend to overproduce the far-infrared (FIR) CBR detected by COBE/FIRAS. On the other hand, our model predicts that the mid-infrared (MIR) flux from warm/nonequilibrium dust is relatively weak in such galaxies making FIR CBR, and this effect reconciles the prima facie conflict between the upper limit on MIR CBR from TeV gamma

Blooming Trees: Substructures and Surrounding Groups of Galaxy Clusters

NASA Astrophysics Data System (ADS)

Yu, Heng; Diaferio, Antonaldo; Serra, Ana Laura; Baldi, Marco

2018-06-01

We develop the Blooming Tree Algorithm, a new technique that uses spectroscopic redshift data alone to identify the substructures and the surrounding groups of galaxy clusters, along with their member galaxies. Based on the estimated binding energy of galaxy pairs, the algorithm builds a binary tree that hierarchically arranges all of the galaxies in the field of view. The algorithm searches for buds, corresponding to gravitational potential minima on the binary tree branches; for each bud, the algorithm combines the number of galaxies, their velocity dispersion, and their average pairwise distance into a parameter that discriminates between the buds that do not correspond to any substructure or group, and thus eventually die, and the buds that correspond to substructures and groups, and thus bloom into the identified structures. We test our new algorithm with a sample of 300 mock redshift surveys of clusters in different dynamical states; the clusters are extracted from a large cosmological N-body simulation of a ΛCDM model. We limit our analysis to substructures and surrounding groups identified in the simulation with mass larger than 1013 h ‑1 M ⊙. With mock redshift surveys with 200 galaxies within 6 h ‑1 Mpc from the cluster center, the technique recovers 80% of the real substructures and 60% of the surrounding groups; in 57% of the identified structures, at least 60% of the member galaxies of the substructures and groups belong to the same real structure. These results improve by roughly a factor of two the performance of the best substructure identification algorithm currently available, the σ plateau algorithm, and suggest that our Blooming Tree Algorithm can be an invaluable tool for detecting substructures of galaxy clusters and investigating their complex dynamics.

“Direct” Gas-phase Metallicity in Local Analogs of High-redshift Galaxies: Empirical Metallicity Calibrations for High-redshift Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Bian, Fuyan; Kewley, Lisa J.; Dopita, Michael A.

2018-06-01

We study the direct gas-phase oxygen abundance using the well-detected auroral line [O III]λ4363 in the stacked spectra of a sample of local analogs of high-redshift galaxies. These local analogs share the same location as z ∼ 2 star-forming galaxies on the [O III]λ5007/Hβ versus [N II]λ6584/Hα Baldwin–Phillips–Terlevich diagram. This type of analog has the same ionized interstellar medium (ISM) properties as high-redshift galaxies. We establish empirical metallicity calibrations between the direct gas-phase oxygen abundances (7.8< 12+{log}({{O}}/{{H}})< 8.4) and the N2 (log([N II]λ6584/Hα))/O3N2 (log(([O III]λ5007/Hβ)/([N II]λ6584/Hα))) indices in our local analogs. We find significant systematic offsets between the metallicity calibrations for our local analogs of high-redshift galaxies and those derived from the local H II regions and a sample of local reference galaxies selected from the Sloan Digital Sky Survey (SDSS). The N2 and O3N2 metallicities will be underestimated by 0.05–0.1 dex relative to our calibration, if one simply applies the local metallicity calibration in previous studies to high-redshift galaxies. Local metallicity calibrations also cause discrepancies of metallicity measurements in high-redshift galaxies using the N2 and O3N2 indicators. In contrast, our new calibrations produce consistent metallicities between these two indicators. We also derive metallicity calibrations for R23 (log(([O III]λλ4959,5007+[O II]λλ3726,3729)/Hβ)), O32(log([O III]λλ4959,5007/[O II]λλ3726,3729)), {log}([O III]λ5007/Hβ), and log([Ne III]λ3869/[O II]λ3727) indices in our local analogs, which show significant offset compared to those in the SDSS reference galaxies. By comparing with MAPPINGS photoionization models, the different empirical metallicity calibration relations in the local analogs and the SDSS reference galaxies can be shown to be primarily due to the change of ionized ISM conditions. Assuming that temperature structure

A Submillimeter Survey of Dust Continuum Emission in Local Dust-Obscured Galaxies

NASA Astrophysics Data System (ADS)

Lee, Jong Chul; Hwang, Ho Seong; Lee, Gwang-Ho

2015-08-01

Dusty star-forming galaxies are responsible for the bulk of cosmic star formation at 1galaxies is far from clear because of their extreme distances. The study of their local analogs helps us to improve understanding of the drivers of the intense star formation activity at high redshift. The submillimeter data on the 'Rayleigh-Jeans' side of the infrared spectral energy distributions (SEDs) of these galaxies are crucial for deriving the physical parameters of the dust content. We therefore conduct a submillimeter survey of local dust-obscured galaxies (DOGs) with the Caltech Submillimeter Observatory and the Submillimeter Array to study their dust properties. We determine the dust masses and temperatures for 16 local DOGs from the SED fit, and compare them with other dusty galaxies to understand a possible evolutionary link among them.

Assessing colour-dependent occupation statistics inferred from galaxy group catalogues

NASA Astrophysics Data System (ADS)

Campbell, Duncan; van den Bosch, Frank C.; Hearin, Andrew; Padmanabhan, Nikhil; Berlind, Andreas; Mo, H. J.; Tinker, Jeremy; Yang, Xiaohu

2015-09-01

We investigate the ability of current implementations of galaxy group finders to recover colour-dependent halo occupation statistics. To test the fidelity of group catalogue inferred statistics, we run three different group finders used in the literature over a mock that includes galaxy colours in a realistic manner. Overall, the resulting mock group catalogues are remarkably similar, and most colour-dependent statistics are recovered with reasonable accuracy. However, it is also clear that certain systematic errors arise as a consequence of correlated errors in group membership determination, central/satellite designation, and halo mass assignment. We introduce a new statistic, the halo transition probability (HTP), which captures the combined impact of all these errors. As a rule of thumb, errors tend to equalize the properties of distinct galaxy populations (i.e. red versus blue galaxies or centrals versus satellites), and to result in inferred occupation statistics that are more accurate for red galaxies than for blue galaxies. A statistic that is particularly poorly recovered from the group catalogues is the red fraction of central galaxies as a function of halo mass. Group finders do a good job in recovering galactic conformity, but also have a tendency to introduce weak conformity when none is present. We conclude that proper inference of colour-dependent statistics from group catalogues is best achieved using forward modelling (i.e. running group finders over mock data) or by implementing a correction scheme based on the HTP, as long as the latter is not too strongly model dependent.

The Redshift Completeness of Local Galaxy Catalogs

NASA Astrophysics Data System (ADS)

Kulkarni, S. R.; Perley, D. A.; Miller, A. A.

2018-06-01

There is considerable interest in understanding the demographics of galaxies within the local universe (defined, for our purposes, as the volume within a radius of 200 Mpc or z ≤ 0.05). In this pilot paper, using supernovae (SNe) as signposts to galaxies, we investigate the redshift completeness of catalogs of nearby galaxies. In particular, type Ia SNe are bright and are good tracers of the bulk of the galaxy population, as they arise in both old and young stellar populations. Our input sample consists of SNe with redshift ≤0.05, discovered by the flux-limited ASAS-SN survey. We define the redshift completeness fraction (RCF) as the number of SN host galaxies with known redshift prior to SN discovery, determined, in this case, via the NASA Extragalactic Database, divided by the total number of newly discovered SNe. Using SNe Ia, we find {RCF}=78{+/- }76% (90% confidence interval) for z < 0.03. We examine the distribution of host galaxies with and without cataloged redshifts as a function of absolute magnitude and redshift, and, unsurprisingly, find that higher-z and fainter hosts are less likely to have a known redshift prior to the detection of the SN. However, surprisingly, some {L}* galaxies are also missing. We conclude with thoughts on the future improvement of RCF measurements that will be made possible from large SN samples resulting from ongoing and especially upcoming time-domain surveys.

Infalling groups and galaxy transformations in the cluster A2142

NASA Astrophysics Data System (ADS)

Einasto, Maret; Deshev, Boris; Lietzen, Heidi; Kipper, Rain; Tempel, Elmo; Park, Changbom; Gramann, Mirt; Heinämäki, Pekka; Saar, Enn; Einasto, Jaan

2018-03-01

Context. Superclusters of galaxies provide dynamical environments for the study of the formation and evolution of structures in the cosmic web from galaxies, to the richest galaxy clusters, and superclusters themselves. Aims: We study galaxy populations and search for possible merging substructures in the rich galaxy cluster A2142 in the collapsing core of the supercluster SCl A2142, which may give rise to radio and X-ray structures in the cluster, and affect galaxy properties of this cluster. Methods: We used normal mixture modelling to select substructure of the cluster A2142. We compared alignments of the cluster, its brightest galaxies (hereafter BCGs), subclusters, and supercluster axes. The projected phase space (PPS) diagram and clustercentric distributions are used to analyse the dynamics of the cluster and study the distribution of various galaxy populations in the cluster and subclusters. Results: We find several infalling galaxy groups and subclusters. The cluster, supercluster, BCGs, and one infalling subcluster are all aligned. Their orientation is correlated with the alignment of the radio and X-ray haloes of the cluster. Galaxy populations in the main cluster and in the outskirts subclusters are different. Galaxies in the centre of the main cluster at the clustercentric distances 0.5 h-1 Mpc (Dc/Rvir < 0.5, Rvir = 0.9 h-1 Mpc) have older stellar populations (with the median age of 10-11 Gyr) than galaxies at larger clustercentric distances. Star-forming and recently quenched galaxies are located mostly at the clustercentric distances Dc ≈ 1.8 h-1 Mpc, where subclusters fall into the cluster and the properties of galaxies change rapidly. In this region the median age of stellar populations of galaxies is about 2 Gyr. Galaxies in A2142 on average have higher stellar masses, lower star formation rates, and redder colours than galaxies in rich groups. The total mass in infalling groups and subclusters is M ≈ 6 × 1014 h-1 M⊙, that is approximately

An X-Ray Atlas of Groups of Galaxies

NASA Technical Reports Server (NTRS)

Mulchaey, John S.; Davis, David S.; Mushotzky, Richard F.; Burnstein, David

2003-01-01

A search was conducted for a hot intragroup medium in 10(exp 9) low-redshift galaxy groups observed with the ROSAT PSPC. Evidence for diffuse, extended X-ray emission is found in at least 61 groups. Approximately one-third of these detections have not been previously reported in the literature. Most of the groups are detected out to less than half of the virial radius with ROSAT. Although some spiral-rich groups do contain an intragroup medium, diffuse emission is restricted to groups that contain at least one early-type galaxy.

The HI Content of Galaxies as a Function of Local Density and Large-Scale Environment

NASA Astrophysics Data System (ADS)

Thoreen, Henry; Cantwell, Kelly; Maloney, Erin; Cane, Thomas; Brough Morris, Theodore; Flory, Oscar; Raskin, Mark; Crone-Odekon, Mary; ALFALFA Team

2017-01-01

We examine the HI content of galaxies as a function of environment, based on a catalogue of 41527 galaxies that are part of the 70% complete Arecibo Legacy Fast-ALFA (ALFALFA) survey. We use nearest-neighbor methods to characterize local environment, and a modified version of the algorithm developed for the Galaxy and Mass Assembly (GAMA) survey to classify large-scale environment as group, filament, tendril, or void. We compare the HI content in these environments using statistics that include both HI detections and the upper limits on detections from ALFALFA. The large size of the sample allows to statistically compare the HI content in different environments for early-type galaxies as well as late-type galaxies. This work is supported by NSF grants AST-1211005 and AST-1637339, the Skidmore Faculty-Student Summer Research program, and the Schupf Scholars program.

A Catalog of Visually Classified Galaxies in the Local (z ∼ 0.01) Universe

NASA Astrophysics Data System (ADS)

Ann, H. B.; Seo, Mira; Ha, D. K.

2015-04-01

The morphological types of 5836 galaxies were classified by a visual inspection of color images using the Sloan Digital Sky Survey Data Release 7 to produce a morphology catalog of a representative sample of local galaxies with z\\lt 0.01. The sample galaxies are almost complete for galaxies brighter than {{r}pet}=17.77. Our classification system is basically the same as that of the Third Reference Catalog of Bright Galaxies with some simplifications for giant galaxies. On the other hand, we distinguish the fine features of dwarf elliptical (dE)-like galaxies to classify five subtypes: dE, blue-cored dwarf ellipticals, dwarf spheroidals (dSph), blue dwarf ellipticals (dEblue), and dwarf lenticulars (dS0). In addition, we note the presence of nucleation in dE, dSph, and dS0. Elliptical galaxies and lenticular galaxies contribute only ∼ 1.5 and ∼ 4.9% of local galaxies, respectively, whereas spirals and irregulars contribute ∼ 32.1 and ∼ 42.8%, respectively. The dEblue galaxies, which are a recently discovered population of galaxies, contribute a significant fraction of dwarf galaxies. There seem to be structural differences between dSph and dE galaxies. The dSph galaxies are fainter and bluer with a shallower surface brightness gradient than dE galaxies. They also have a lower fraction of galaxies with small axis ratios (b/a≲ 0.4) than dE galaxies. The mean projected distance to the nearest neighbor galaxy is ∼260 kpc. About 1% of local galaxies have no neighbors with comparable luminosity within a projected distance of 2 Mpc.

Search for Dark Matter Annihilation in Galaxy Groups

NASA Astrophysics Data System (ADS)

Lisanti, Mariangela; Mishra-Sharma, Siddharth; Rodd, Nicholas L.; Safdi, Benjamin R.

2018-03-01

We use 413 weeks of publicly available Fermi Pass 8 gamma-ray data combined with recently developed galaxy group catalogs to search for evidence of dark matter annihilation in extragalactic halos. In our study, we use luminosity-based mass estimates and mass-to-concentration relations to infer the J factors and associated uncertainties for hundreds of galaxy groups within a redshift range z ≲0.03 . We employ a conservative substructure boost factor model, which only enhances the sensitivity by an O (1 ) factor. No significant evidence for dark matter annihilation is found, and we exclude thermal relic cross sections for dark matter masses below ˜30 GeV to 95% confidence in the b b ¯ annihilation channel. These bounds are comparable to those from Milky Way dwarf spheroidal satellite galaxies. The results of our analysis increase the tension but do not rule out the dark matter interpretation of the Galactic Center excess. We provide a catalog of the galaxy groups used in this study and their inferred properties, which can be broadly applied to searches for extragalactic dark matter.

Search for Dark Matter Annihilation in Galaxy Groups.

PubMed

Lisanti, Mariangela; Mishra-Sharma, Siddharth; Rodd, Nicholas L; Safdi, Benjamin R

2018-03-09

We use 413 weeks of publicly available Fermi Pass 8 gamma-ray data combined with recently developed galaxy group catalogs to search for evidence of dark matter annihilation in extragalactic halos. In our study, we use luminosity-based mass estimates and mass-to-concentration relations to infer the J factors and associated uncertainties for hundreds of galaxy groups within a redshift range z≲0.03. We employ a conservative substructure boost factor model, which only enhances the sensitivity by an O(1) factor. No significant evidence for dark matter annihilation is found, and we exclude thermal relic cross sections for dark matter masses below ∼30  GeV to 95% confidence in the bb[over ¯] annihilation channel. These bounds are comparable to those from Milky Way dwarf spheroidal satellite galaxies. The results of our analysis increase the tension but do not rule out the dark matter interpretation of the Galactic Center excess. We provide a catalog of the galaxy groups used in this study and their inferred properties, which can be broadly applied to searches for extragalactic dark matter.

Galaxy Tagging: photometric redshift refinement and group richness enhancement

NASA Astrophysics Data System (ADS)

Kafle, P. R.; Robotham, A. S. G.; Driver, S. P.; Deeley, S.; Norberg, P.; Drinkwater, M. J.; Davies, L. J.

2018-06-01

We present a new scheme, galtag, for refining the photometric redshift measurements of faint galaxies by probabilistically tagging them to observed galaxy groups constructed from a brighter, magnitude-limited spectroscopy survey. First, this method is tested on the DESI light-cone data constructed on the GALFORM galaxy formation model to tests its validity. We then apply it to the photometric observations of galaxies in the Kilo-Degree Imaging Survey (KiDS) over a 1 deg2 region centred at 15h. This region contains Galaxy and Mass Assembly (GAMA) deep spectroscopic observations (i-band<22) and an accompanying group catalogue to r-band<19.8. We demonstrate that even with some trade-off in sample size, an order of magnitude improvement on the accuracy of photometric redshifts is achievable when using galtag. This approach provides both refined photometric redshift measurements and group richness enhancement. In combination these products will hugely improve the scientific potential of both photometric and spectroscopic datasets. The galtag software will be made publicly available at https://github.com/pkaf/galtag.git.

VizieR Online Data Catalog: Friends-of-friends galaxy group finder (Tempel+, 2016)

NASA Astrophysics Data System (ADS)

Tempel, E.; Kipper, R.; Tamm, A.; Gramann, M.; Einasto, M.; Sepp, T.; Tuvikene, T.

2016-01-01

To delineate galaxy groups in the local Universe, we used galaxy data from the extragalactic distance database (EDD2; Tully et al., 2009AJ....138..323T). The sample encompasses three datasets. As the main source, we used the Two Micron All Sky Survey (Skrutskie et al. 2006AJ....131.1163S, Cat. VII/233) Redshift Survey (2MRS) galaxies brighter than 11.75 mag in the Ks band (for a description of the catalogue, see Huchra et al., 2012, Cat. J/ApJS/199/26). We only used galaxies that are securely off the Galactic plane: Galactic latitude |b|>5°. Since the galaxy sample becomes extremely sparse farther away, we only used galaxies with a cosmic microwave background (CMB) corrected redshift z=0...0.1 (up to 430Mpc). This selection restricts our 2MRS sample to 43480 galaxies. For our analysis, we complemented the main 2MRS sample with two other sources. From the CosmicFlows-2 survey that contains 8198 galaxies with redshift-independent distance estimates (CF2; Tully et al., 2013, Cat. J/AJ/146/86), we added 3627 (of these, 2799 galaxies do not have a measured Ks magnitude). In addition, we made use of the 2M++ catalogue Lavaux & Hudson (2011, Cat. J/MNRAS/416/2840), which combines elements from the 2MRS, the 6DF Galaxy Survey (Jones et al. 2009MNRAS.399..683J, Cat. VII/259), and the Sloan Digital Sky Survey (York et al., 2000AJ....120.1579Y). Of the 64745 galaxies of the 2M++, we added 31271 galaxies down to Ks<12.54, which extends the sample well beyond the 2MRS magnitude limit. Our final galaxy dataset includes 78378 galaxies. (4 data files).

Detailed photometric analysis of young star groups in the galaxy NGC 300

NASA Astrophysics Data System (ADS)

Rodríguez, M. J.; Baume, G.; Feinstein, C.

2016-10-01

obtained from the size distribution are both 25 pc, in agreement with the value for the Local Group and nearby galaxies. Additionally, we found an average PDMF slope that is compatible with the Salpeter value. Full Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/594/A34

Galaxy clusters in simulations of the local Universe: a matter of constraints

NASA Astrophysics Data System (ADS)

Sorce, Jenny G.; Tempel, Elmo

2018-06-01

To study the full formation and evolution history of galaxy clusters and their population, high-resolution simulations of the latter are flourishing. However, comparing observed clusters to the simulated ones on a one-to-one basis to refine the models and theories down to the details is non-trivial. The large variety of clusters limits the comparisons between observed and numerical clusters. Simulations resembling the local Universe down to the cluster scales permit pushing the limit. Simulated and observed clusters can be matched on a one-to-one basis for direct comparisons provided that clusters are well reproduced besides being in the proper large-scale environment. Comparing random and local Universe-like simulations obtained with differently grouped observational catalogues of peculiar velocities, this paper shows that the grouping scheme used to remove non-linear motions in the catalogues that constrain the simulations affects the quality of the numerical clusters. With a less aggressive grouping scheme - galaxies still falling on to clusters are preserved - combined with a bias minimization scheme, the mass of the dark matter haloes, simulacra for five local clusters - Virgo, Centaurus, Coma, Hydra, and Perseus - is increased by 39 per cent closing the gap with observational mass estimates. Simulacra are found on average in 89 per cent of the simulations, an increase of 5 per cent with respect to the previous grouping scheme. The only exception is Perseus. Since the Perseus-Pisces region is not well covered by the used peculiar velocity catalogue, the latest release lets us foresee a better simulacrum for Perseus in a near future.

On the Formation of Elliptical Galaxies via Mergers in Galaxy Groups

NASA Astrophysics Data System (ADS)

Taranu, Dan; Dubinski, John; Yee, Howard K. C.

2015-01-01

Giant elliptical galaxies have long been thought to form through gas-rich "major" mergers of two roughly equal-mass spiral galaxies. However, elliptical galaxies are often found at the centers of groups, and so are likely to have undergone several significant mergers. We test the hypothesis that ellipticals form through multiple, mainly minor and dry mergers in groups, using a novel sample of hundreds of N-body simulations of mergers in groups of three to twenty-five spiral galaxies.Realistic mock observations of the simulated central merger remnants show that they have comparable surface brightness profiles to observed ellipticals from SDSS and ATLAS3D - so long as the progenitor spirals begin with concentrated bulges. The remnants follow tight size-luminosity and velocity dispersion-luminosity relations (<0.12 dex scatter), with similar slopes as observed. Stochastic merging can produce tight scaling relations if the merging galaxies follow tight scaling relations themselves. However, the remnants are too large and have too low dispersions at fixed luminosity. Some remnants show substantial (v/σ > 0.1) rotational support, but most are slow rotators with v/σ << 0.5.Ellipticals also follow a tight "fundamental plane" scaling relation between size R, mean surface brightness μ and velocity dispersion σ: R ∝ σaμb, with small (<0.06 dex) scatter and significantly different coefficients from the expected scaling (a "tilt"). The remnants lie on a similar fundamental plane, with even smaller scatter (0.02 dex), as well as a tilt in the correct sense - albeit weaker than observed. This tilt is mainly driven by variable dark matter fractions within Reff, such that massive merger remnants have larger central dark matter fractions than their lower-mass counterparts.These results suggest that massive ellipticals can originate from multiple, mainly minor and dry mergers. However, significant gas dissipation may be needed to produce lower-mass, rapidly

Galaxy Zoo: the interplay of quenching mechanisms in the group environment★

NASA Astrophysics Data System (ADS)

Smethurst, R. J.; Lintott, C. J.; Bamford, S. P.; Hart, R. E.; Kruk, S. J.; Masters, K. L.; Nichol, R. C.; Simmons, B. D.

2017-08-01

Does the environment of a galaxy directly influence the quenching history of a galaxy? Here, we investigate the detailed morphological structures and star formation histories of a sample of SDSS group galaxies with both classifications from Galaxy Zoo 2 and near ultra-violet (NUV) detections in GALEX. We use the optical and NUV colours to infer the quenching time and rate describing a simple exponentially declining star formation history for each galaxy, along with a control sample of field galaxies. We find that the time since quenching and the rate of quenching do not correlate with the relative velocity of a satellite but are correlated with the group potential. This quenching occurs within an average quenching time-scale of ˜ 2.5 Gyr from star forming to complete quiescence, during an average infall time (from ˜10R200 to 0.01R200) of ˜ 2.6 Gyr. Our results suggest that the environment does play a direct role in galaxy quenching through quenching mechanisms that are correlated with the group potential, such as harassment, interactions or starvation. Environmental quenching mechanisms that are correlated with satellite velocity, such as ram-pressure stripping, are not the main cause of quenching in the group environment. We find that no single mechanism dominates over another, except in the most extreme environments or masses. Instead, an interplay of mergers, mass and morphological quenching and environment-driven quenching mechanisms dependent on the group potential drive galaxy evolution in groups.

Undergraduate ALFALFA Team: Star Formation in the NGC 5846 Group of Galaxies

NASA Astrophysics Data System (ADS)

Viani, Lucas; Koopmann, R. A.; Darling, H.; ALFALFA Team

2013-01-01

We examine gas and star formation properties of galaxies in the NGC 5846 group. Narrowband Halpha and broadband R images for a sample of galaxies were obtained at the KPNO WIYN 0.9m with MOSAIC and the SMARTS 0.9m telescope at CTIO. Neutral hydrogen data from the Arecibo Legacy Fast ALFA (ALFALFA) survey trace the cold neutral gas content. The amounts and extents of star formation in a subsample of galaxies are compared as a function of cold gas content and position in the group. The typical star formation rates and extents of NGC 5846 galaxies are less than those of isolated galaxies and similar to those of galaxies located in the Virgo Cluster and other group environments. This work is part of the Undergraduate ALFALFA (Arecibo Legacy Fast ALFA) Team Groups Project, a collaborative undertaking of faculty and undergraduates at 11 institutions, aimed at investigating properties of galaxy groups surveyed by the ALFALFA blind HI survey.

THE ZURICH ENVIRONMENTAL STUDY OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. I. WHICH ENVIRONMENT AFFECTS GALAXY EVOLUTION?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carollo, C. Marcella; Cibinel, Anna; Lilly, Simon J.

2013-10-20

The Zurich Environmental Study (ZENS) is based on a sample of ∼1500 galaxy members of 141 groups in the mass range ∼10{sup 12.5-14.5} M{sub ☉} within the narrow redshift range 0.05 < z < 0.0585. ZENS adopts novel approaches, described here, to quantify four different galactic environments, namely: (1) the mass of the host group halo; (2) the projected halo-centric distance; (3) the rank of galaxies as central or satellites within their group halos; and (4) the filamentary large-scale structure density. No self-consistent identification of a central galaxy is found in ∼40% of <10{sup 13.5} M{sub ☉} groups, from whichmore » we estimate that ∼15% of groups at these masses are dynamically unrelaxed systems. Central galaxies in relaxed and unrelaxed groups generally have similar properties, suggesting that centrals are regulated by their mass and not by their environment. Centrals in relaxed groups have, however, ∼30% larger sizes than in unrelaxed groups, possibly due to accretion of small satellites in virialized group halos. At M > 10{sup 10} M{sub ☉}, satellite galaxies in relaxed and unrelaxed groups have similar size, color, and (specific) star formation rate distributions; at lower galaxy masses, satellites are marginally redder in relaxed relative to unrelaxed groups, suggesting quenching of star formation in low-mass satellites by physical processes active in relaxed halos. Overall, relaxed and unrelaxed groups show similar stellar mass populations, likely indicating similar stellar mass conversion efficiencies. In the enclosed ZENS catalog, we publish all environmental diagnostics as well as the galaxy structural and photometric measurements described in companion ZENS papers II and III.« less

Dark energy in the environments of the Local Group, the M 81 group, and the CenA group: the normalized Hubble diagram

NASA Astrophysics Data System (ADS)

Teerikorpi, P.; Chernin, A. D.; Karachentsev, I. D.; Valtonen, M. J.

2008-05-01

Context: Type Ia supernova observations on scales of thousands of Mpc show that the global expansion of the universe is accelerated by antigravity produced by the enigmatic dark energy contributing 3/4 of the total energy of the universe. Aims: Does antigravity act on small scales as well as large? As a continuation of our efforts to answer this crucial question we combine high accuracy observations of the galaxy flows around the Local Group and the nearby M 81 and CenA groups to observe the effect of the dark energy density on local scales of a few Mpc. Methods: We use an analytical model to describe non-uniform static space-time regions around galaxy groups. In this context it is useful to present the Hubble flow in a normalized Hubble diagram V/Hv Rv vs. r/R_v, where the vacuum Hubble constant Hv depends only on the cosmological vacuum density and the zero-gravity distance Rv depends on the vacuum density and on the mass of the galaxy group. We have prepared the normalized Hubble diagrams for the LG, M 81 and CenA group environments for different values of the assumed vacuum energy density, using a total of about 150 galaxies, for almost all of which the distances have been measured by the HST. Results: The normalized Hubble diagram, where we identify dynamically different regions, is in agreement with the standard vacuum density (Ωv = 0.77~h_70-2), the out-flow of galaxies clearly being controlled by the minimum energy condition imposed by the central mass plus the vacuum density. A high vacuum density 1.6~h_70-2 violates the minimum energy limit, while a low density 0.1~h_70-2 leaves the start of the Hubble flow around 1-2 Mpc with the slope close to the global value obscure. We also consider the subtle relation of the zero-gravity radius Rv to the zero-velocity distance R0 appearing in the usual retarded expansion around a mass M: in a vacuum-dominated flat universe R0 ≈ 0.76 R_v. Conclusions: The normalized Hubble diagram appears to be a good way to

Near-Field Cosmology with Resolved Stellar Populations Around Local Volume LMC Stellar-Mass Galaxies

NASA Astrophysics Data System (ADS)

Carlin, Jeffrey L.; Sand, David J.; Willman, Beth; Brodie, Jean P.; Crnojevic, Denija; Forbes, Duncan; Hargis, Jonathan R.; Peter, Annika; Pucha, Ragadeepika; Romanowsky, Aaron J.; Spekkens, Kristine; Strader, Jay

2018-06-01

We discuss our ongoing observational program to comprehensively map the entire virial volumes of roughly LMC stellar mass galaxies at distances of ~2-4 Mpc. The MADCASH (Magellanic Analog Dwarf Companions And Stellar Halos) survey will deliver the first census of the dwarf satellite populations and stellar halo properties within LMC-like environments in the Local Volume. Our results will inform our understanding of the recent DES discoveries of dwarf satellites tentatively affiliated with the LMC/SMC system. This program has already yielded the discovery of the faintest known dwarf galaxy satellite of an LMC stellar-mass host beyond the Local Group, based on deep Subaru+HyperSuprimeCam imaging reaching ~2 magnitudes below its TRGB, and at least two additional candidate satellites. We will summarize the survey results and status to date, highlighting some challenges encountered and lessons learned as we process the data for this program through a prototype LSST pipeline. Our program will examine whether LMC stellar mass dwarfs have extended stellar halos, allowing us to assess the relative contributions of in-situ stars vs. merger debris to their stellar populations and halo density profiles. We outline the constraints on galaxy formation models that will be provided by our observations of low-mass galaxy halos and their satellites.

Galaxy And Mass Assembly (GAMA): growing up in a bad neighbourhood - how do low-mass galaxies become passive?

NASA Astrophysics Data System (ADS)

Davies, L. J. M.; Robotham, A. S. G.; Driver, S. P.; Alpaslan, M.; Baldry, I. K.; Bland-Hawthorn, J.; Brough, S.; Brown, M. J. I.; Cluver, M. E.; Holwerda, B. W.; Hopkins, A. M.; Lara-López, M. A.; Mahajan, S.; Moffett, A. J.; Owers, M. S.; Phillipps, S.

2016-02-01

Both theoretical predictions and observations of the very nearby Universe suggest that low-mass galaxies(log10[M*/M⊙] < 9.5) are likely to remain star-forming unless they are affected by their local environment. To test this premise, we compare and contrast the local environment of both passive and star-forming galaxies as a function of stellar mass, using the Galaxy and Mass Assembly survey. We find that passive fractions are higher in both interacting pair and group galaxies than the field at all stellar masses, and that this effect is most apparent in the lowest mass galaxies. We also find that essentially all passive log10[M*/M⊙] < 8.5 galaxies are found in pair/group environments, suggesting that local interactions with a more massive neighbour cause them to cease forming new stars. We find that the effects of immediate environment (local galaxy-galaxy interactions) in forming passive systems increase with decreasing stellar mass, and highlight that this is potentially due to increasing interaction time-scales giving sufficient time for the galaxy to become passive via starvation. We then present a simplistic model to test this premise, and show that given our speculative assumptions, it is consistent with our observed results.

Quantitative Spectroscopy of Supergiants in the Local Group Dwarf Galaxy IC 1613: Metallicity and Distance

NASA Astrophysics Data System (ADS)

Berger, Travis A.; Kudritzki, Rolf-Peter; Urbaneja, Miguel A.; Bresolin, Fabio; Gieren, Wolfgang; Pietrzyński, Grzegorz; Przybilla, Norbert

2018-06-01

We present a spectral analysis of 21 blue supergiant stars of spectral types late B to early A within the Local Group dwarf galaxy IC 1613, based on VLT Focal Reducer and Low Dispersion Spectrograph 2 low-resolution spectra. Combining our results with studies of early B-type blue supergiants, we report a wide bimodal distribution of metallicities with two peaks around [Z] ∼ ‑0.50 dex and [Z] ∼ ‑0.85 dex. The bimodal distribution correlates with spatial location, when compared with column densities of neutral hydrogen in IC 1613. While the low [Z] objects appear in regions of relatively high ISM H I column densities or close to them, the high [Z] supergiants are found in the central H I hole that is almost devoid of hydrogen. This suggests there are varied chemical evolution histories for the young stellar populations in IC 1613. Utilizing the flux-weighted gravity–luminosity relation, we determine IC 1613's distance modulus as m ‑ M = 24.39 ± 0.11 mag. This value is in agreement within previous distance measurements using the near-infrared period–luminosity relationship of Cepheids and the tip of the red giant branch.

Where are compact groups in the local Universe?

NASA Astrophysics Data System (ADS)

Díaz-Giménez, Eugenia; Zandivarez, Ariel

2015-06-01

Aims: The purpose of this work is to perform a statistical analysis of the location of compact groups in the Universe from observational and semi-analytical points of view. Methods: We used the velocity-filtered compact group sample extracted from the Two Micron All Sky Survey for our analysis. We also used a new sample of galaxy groups identified in the 2M++ galaxy redshift catalogue as tracers of the large-scale structure. We defined a procedure to search in redshift space for compact groups that can be considered embedded in other overdense systems and applied this criterion to several possible combinations of different compact and galaxy group subsamples. We also performed similar analyses for simulated compact and galaxy groups identified in a 2M++ mock galaxy catalogue constructed from the Millennium Run Simulation I plus a semi-analytical model of galaxy formation. Results: We observed that only ~27% of the compact groups can be considered to be embedded in larger overdense systems, that is, most of the compact groups are more likely to be isolated systems. The embedded compact groups show statistically smaller sizes and brighter surface brightnesses than non-embedded systems. No evidence was found that embedded compact groups are more likely to inhabit galaxy groups with a given virial mass or with a particular dynamical state. We found very similar results when the analysis was performed using mock compact and galaxy groups. Based on the semi-analytical studies, we predict that 70% of the embedded compact groups probably are 3D physically dense systems. Finally, real space information allowed us to reveal the bimodal behaviour of the distribution of 3D minimum distances between compact and galaxy groups. Conclusions: The location of compact groups should be carefully taken into account when comparing properties of galaxies in environments that are a priori different. Appendices are available in electronic form at http://www.aanda.orgFull Tables B.1 and B.2

A Bridge from Optical to Infrared Galaxies: Explaining Local Properties, Predicting Galaxy Counts and the Cosmic Background Radiation

NASA Astrophysics Data System (ADS)

Totani, T.; Takeuchi, T. T.

2001-12-01

A new model of infrared galaxy counts and the cosmic background radiation (CBR) is developed by extending a model for optical/near-infrared galaxies. Important new characteristics of this model are that mass scale dependence of dust extinction is introduced based on the size-luminosity relation of optical galaxies, and that the big grain dust temperature T dust is calculated based on a physical consideration for energy balance, rather than using the empirical relation between T dust and total infrared luminosity L IR found in local galaxies, which has been employed in most of previous works. Consequently, the local properties of infrared galaxies, i.e., optical/infrared luminosity ratios, L IR-T dust correlation, and infrared luminosity function are outputs predicted by the model, while these have been inputs in a number of previous models. Our model indeed reproduces these local properties reasonably well. Then we make predictions for faint infrared counts (in 15, 60, 90, 170, 450, and 850 μ m) and CBR by this model. We found considerably different results from most of previous works based on the empirical L IR-T dust relation; especially, it is shown that the dust temperature of starbursting primordial elliptical galaxies is expected to be very high (40--80K). This indicates that intense starbursts of forming elliptical galaxies should have occurred at z ~ 2--3, in contrast to the previous results that significant starbursts beyond z ~ 1 tend to overproduce the far-infrared (FIR) CBR detected by COBE/FIRAS. On the other hand, our model predicts that the mid-infrared (MIR) flux from warm/nonequilibrium dust is relatively weak in such galaxies making FIR CBR, and this effect reconciles the prima facie conflict between the upper limit on MIR CBR from TeV gamma-ray observations and the COBE\\ detections of FIR CBR. The authors thank the financial support by the Japan Society for Promotion of Science.

Distributions of Gas and Galaxies from Galaxy Clusters to Larger Scales

NASA Astrophysics Data System (ADS)

Patej, Anna

2017-01-01

We address the distributions of gas and galaxies on three scales: the outskirts of galaxy clusters, the clustering of galaxies on large scales, and the extremes of the galaxy distribution. In the outskirts of galaxy clusters, long-standing analytical models of structure formation and recent simulations predict the existence of density jumps in the gas and dark matter profiles. We use these features to derive models for the gas density profile, obtaining a simple fiducial model that is in agreement with both observations of cluster interiors and simulations of the outskirts. We next consider the galaxy density profiles of clusters; under the assumption that the galaxies in cluster outskirts follow similar collisionless dynamics as the dark matter, their distribution should show a steep jump as well. We examine the profiles of a low-redshift sample of clusters and groups, finding evidence for the jump in some of these clusters. Moving to larger scales where massive galaxies of different types are expected to trace the same large-scale structure, we present a test of this prediction by measuring the clustering of red and blue galaxies at z 0.6, finding low stochasticity between the two populations. These results address a key source of systematic uncertainty - understanding how target populations of galaxies trace large-scale structure - in galaxy redshift surveys. Such surveys use baryon acoustic oscillations (BAO) as a cosmological probe, but are limited by the expense of obtaining sufficiently dense spectroscopy. With the intention of leveraging upcoming deep imaging data, we develop a new method of detecting the BAO in sparse spectroscopic samples via cross-correlation with a dense photometric catalog. This method will permit the extension of BAO measurements to higher redshifts than possible with the existing spectroscopy alone. Lastly, we connect galaxies near and far: the Local Group dwarfs and the high redshift galaxies observed by Hubble and Spitzer. We

Clustering of local group distances: Publication bias or correlated measurements? II. M31 and beyond

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Grijs, Richard; Bono, Giuseppe

2014-07-01

The accuracy of extragalactic distance measurements ultimately depends on robust, high-precision determinations of the distances to the galaxies in the local volume. Following our detailed study addressing possible publication bias in the published distance determinations to the Large Magellanic Cloud (LMC), here we extend our distance range of interest to include published distance moduli to M31 and M33, as well as to a number of their well-known dwarf galaxy companions. We aim at reaching consensus on the best, most homogeneous, and internally most consistent set of Local Group distance moduli to adopt for future, more general use based on themore » largest set of distance determinations to individual Local Group galaxies available to date. Based on a careful, statistically weighted combination of the main stellar population tracers (Cepheids, RR Lyrae variables, and the magnitude of the tip of the red-giant branch), we derive a recommended distance modulus to M31 of (m−M){sub 0}{sup M31}=24.46±0.10 mag—adopting as our calibration an LMC distance modulus of (m−M){sub 0}{sup LMC}=18.50 mag—and a fully internally consistent set of benchmark distances to key galaxies in the local volume, enabling us to establish a robust and unbiased, near-field extragalactic distance ladder.« less

Dust Properties of Local Dust-obscured Galaxies with the Submillimeter Array

NASA Astrophysics Data System (ADS)

Hwang, Ho Seong; Andrews, Sean M.; Geller, Margaret J.

2013-11-01

We report Submillimeter Array observations of the 880 μm dust continuum emission for four dust-obscured galaxies (DOGs) in the local universe. Two DOGs are clearly detected with S ν(880 μm) =10-13 mJy and S/N > 5, but the other two are not detected with 3σ upper limits of S ν(880 μm) =5-9 mJy. Including an additional two local DOGs with submillimeter data from the literature, we determine the dust masses and temperatures for six local DOGs. The infrared luminosities and dust masses for these DOGs are in the ranges of 1.2-4.9 × 1011(L ⊙) and 4-14 × 107(M ⊙), respectively. The dust temperatures derived from a two-component modified blackbody function are 23-26 K and 60-124 K for the cold and warm dust components, respectively. Comparison of local DOGs with other infrared luminous galaxies with submillimeter detections shows that the dust temperatures and masses do not differ significantly among these objects. Thus, as argued previously, local DOGs are not a distinctive population among dusty galaxies, but simply represent the high-end tail of the dust obscuration distribution.

Searching for intermediate groups of galaxies with Suzaku in Bootes field

NASA Astrophysics Data System (ADS)

Tawara, Yuzuru; Mitsuishi, Ikuyuki

2016-07-01

To investigate redshift evolution of groups of galaxies is significant also in terms of galaxy evolution. Recent observational studies show that an AGN fraction and a magnitude gap between the first and the second brightest group galaxies increase in group environments at lower redshifts (Oh et al. 2014 & Gozaliasl et al. 2014). Thus, comprehension for the evolution of the systems will bring us to hints on both morphological evolution of galaxies and galaxy-galaxy interactions. However, observational samples of groups of galaxies at higher redshifts are limited due to its low flux and surface brightness. Thus, we aimed at searching for new samples using both X-ray and optical data. To identify the group systems at higher redshifts, deep optical imaging and spectroscopic data are needed. Bootes field is one of the best regions for this purpose because there are up to 17 bands of data available per source from infrared, optical, UV, and X-ray (e.g., Kenter et al. 2005, Chung et al. 2014). XBootes survey was conducted in 2003 using Chandra (Murray et al. 2005) and X-ray extended sources were detected around intermediate optically-identified groups of galaxies even though Chandra could not reveal their origins due to poor photon statistics. Thus, we conducted X-ray follow-up observations using Suzaku which has low and stable background and thus is optimum for such low surface brightness sources for brightest 6 group candidates with redshifts of 0.15-0.42. Consequently, Suzaku detected excess emissions from all the targets in their images and spectral analysis reveals that 6 sources are originated from group- or poor-cluster-scale halos with temperatures, abundances and luminosities of 1.6-3.0 keV, <0.3 solar and ~1044 erg s-1, respectively. In this conference, we will report on the details of our analysis and results using multiwavelength data such as radio, optical and X-ray to examine the AGN fractions and magnitude gaps in our samples and discuss the redshift

Galaxy interactions in compact groups - II. Abundance and kinematic anomalies in HCG 91c

NASA Astrophysics Data System (ADS)

Vogt, Frédéric P. A.; Dopita, Michael A.; Borthakur, Sanchayeeta; Verdes-Montenegro, Lourdes; Heckman, Timothy M.; Yun, Min S.; Chambers, Kenneth C.

2015-07-01

Galaxies in Hickson Compact Group 91 (HCG 91) were observed with the WiFeS integral field spectrograph as part of our ongoing campaign targeting the ionized gas physics and kinematics inside star-forming members of compact groups. Here, we report the discovery of H II regions with abundance and kinematic offsets in the otherwise unremarkable star-forming spiral HCG 91c. The optical emission line analysis of this galaxy reveals that at least three H II regions harbour an oxygen abundance ˜0.15 dex lower than expected from their immediate surroundings and from the abundance gradient present in the inner regions of HCG 91c. The same star-forming regions are also associated with a small kinematic offset in the form of a lag of 5-10 km s-1 with respect to the local circular rotation of the gas. H I observations of HCG 91 from the Very Large Array and broad-band optical images from Pan-STARRS (Panoramic Survey Telescope And Rapid Response System) suggest that HCG 91c is caught early in its interaction with the other members of HCG 91. We discuss different scenarios to explain the origin of the peculiar star-forming regions detected with WiFeS, and show that evidence points towards infalling and collapsing extraplanar gas clouds at the disc-halo interface, possibly as a consequence of long-range gravitational perturbations of HCG 91c from the other group members. As such, HCG 91c provides evidence that some of the perturbations possibly associated with the early phase of galaxy evolution in compact groups impact the star-forming disc locally, and on sub-kpc scales.

The abundance of ultra-diffuse galaxies from groups to clusters. UDGs are relatively more common in more massive haloes

NASA Astrophysics Data System (ADS)

van der Burg, Remco F. J.; Hoekstra, Henk; Muzzin, Adam; Sifón, Cristóbal; Viola, Massimo; Bremer, Malcolm N.; Brough, Sarah; Driver, Simon P.; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Holwerda, Benne W.; Klaes, Dominik; Kuijken, Konrad; McGee, Sean; Nakajima, Reiko; Napolitano, Nicola; Norberg, Peder; Taylor, Edward N.; Valentijn, Edwin

2017-11-01

In recent years, many studies have reported substantial populations of large galaxies with low surface brightness in local galaxy clusters. Various theories that aim to explain the presence of such ultra-diffuse galaxies (UDGs) have since been proposed. A key question that will help to distinguish between models is whether UDGs have counterparts in host haloes with lower masses, and if so, what their abundance as a function of halo mass is. We here extend our previous study of UDGs in galaxy clusters to galaxy groups. We measure the abundance of UDGs in 325 spectroscopically selected groups from the Galaxy And Mass Assembly (GAMA) survey. We make use of the overlapping imaging from the ESO Kilo-Degree Survey (KiDS), from which we can identify galaxies with mean surface brightnesses within their effective radii down to 25.5 mag arcsec-2 in the r band. We are able to measure a significant overdensity of UDGs (with sizes reff ≥ 1.5 kpc) in galaxy groups down to M200 = 1012 M⊙, a regime where approximately only one in ten groups contains a UDG that we can detect. We combine measurements of the abundance of UDGs in haloes that cover three orders of magnitude in halo mass, finding that their numbers scale quite steeply with halo mass: NUDG(R < R200) ∝ M2001.11±0.07. To better interpret this, we also measure the mass-richness relation for brighter galaxies down to Mr* + 2.5 in the same GAMA groups, and find a much shallower relation of NBright(R < R200) ∝ M2000.78±0.05. This shows that compared to bright galaxies, UDGs are relatively more abundant in massive clusters than in groups. We discuss the implications, but it is still unclear whether this difference is related to a higher destruction rate of UDGs in groups or if massive haloes have a positive effect on UDG formation.

Simulating The Dynamical Evolution Of Galaxies In Group And Cluster Environments

NASA Astrophysics Data System (ADS)

Vijayaraghavan, Rukmani

2015-07-01

Galaxy clusters are harsh environments for their constituent galaxies. A variety of physical processes effective in these dense environments transform gas-rich, spiral, star-forming galaxies to elliptical or spheroidal galaxies with very little gas and therefore minimal star formation. The consequences of these processes are well understood observationally. Galaxies in progressively denser environments have systematically declining star formation rates and gas content. However, a theoretical understanding of of where, when, and how these processes act, and the interplay between the various galaxy transformation mechanisms in clusters remains elusive. In this dissertation, I use numerical simulations of cluster mergers as well as galaxies evolving in quiescent environments to develop a theoretical framework to understand some of the physics of galaxy transformation in cluster environments. Galaxies can be transformed in smaller groups before they are accreted by their eventual massive cluster environments, an effect termed `pre-processing'. Galaxy cluster mergers themselves can accelerate many galaxy transformation mechanisms, including tidal and ram pressure stripping of galaxies and galaxy-galaxy collisions and mergers that result in reassemblies of galaxies' stars and gas. Observationally, cluster mergers have distinct velocity and phase-space signatures depending on the observer's line of sight with respect to the merger direction. Using dark matter only as well as hydrodynamic simulations of cluster mergers with random ensembles of particles tagged with galaxy models, I quantify the effects of cluster mergers on galaxy evolution before, during, and after the mergers. Based on my theoretical predictions of the dynamical signatures of these mergers in combination with galaxy transformation signatures, one can observationally identify remnants of mergers and quantify the effect of the environment on galaxies in dense group and cluster environments. The presence of

The Merger History, AGN and Dwarf Galaxies of Hickson Compact Group 59

NASA Technical Reports Server (NTRS)

Konstantopoulos, I. S.; Gallagher, S. C.; Fedotov, K.; Durrell, P. R.; Tzanavaris, P.; Hill, A. R.; Zabludoff, A. I.; Maier, M. L.; Elmegreen, D. M.; Charlton, J. C.;

State-of-the-art multi-wavelength observations of nearby brightest group/cluster galaxies

NASA Astrophysics Data System (ADS)

Gendron-Marsolais, Marie-Lou; Hlavacek-Larrondo, Julie

2018-01-01

Nearby galaxy groups and clusters are crucial to our understanding of the impact of nuclear outbursts on the intracluster medium as their proximity allows us to study in detail the processes of feedback from active galactic nuclei in these systems. In this talk, I will present state-of-the-art multi-wavelength observations signatures of this mechanism.I will first show results on multi-configuration 230-470 MHz observations of the Perseus cluster from the Karl G. Jansky Very Large Array, probing the non-thermal emission from the old particle population of the AGN outflows. These observations reveal a multitude of new structures associated with the “mini-halo” and illustrate the high-quality images that can be obtained with the new JVLA at low radio-frequencies.Second, I will present new observations with the optical imaging Fourier transform spectrometer SITELLE (CFHT) of NGC 1275, the Perseus cluster's brightest galaxy. With its wide field of view, it is the only integral field unit spectroscopy instrument able to cover the large emission-line filamentary nebula in NGC 1275. I will present the first detailed velocity map of this nebula in its entirety and tackle the question of its origin (residual cooling flow or dragged gas).Finally, I will present deep Chandra observations of the nearby early-type massive elliptical galaxy NGC 4472, the most optically luminous galaxy in the local Universe, lying on the outskirts of the Virgo cluster. Enhanced X-ray rims around the radio lobes are detected and interpreted as gas uplifted from the core by the buoyant rise of the radio bubbles. We estimate the energy required to lift the gas to constitute a significant fraction of the total outburst energy.I will thus show how these high-fidelity observations of nearby brightest group/cluster galaxies are improving our understanding of the AGN feedback mechanism taking place in galaxy groups and clusters.

Diffuse hot gas in the NGC 4261 group of galaxies

NASA Technical Reports Server (NTRS)

Davis, David S.; Mushotzky, Richard F.; Mulchaey, John S.; Worrall, D. M.; Birkinshaw, M.; Burstein, David

1995-01-01

We have found diffuse X-ray gas in the group of galaxies containing the elliptical galaxy NGC 4261. This galaxy along with its associated companions are behind the Virgo cluster in the W-cloud. A recent analysis of the velocity structure in the Virgo region indicates that the W-cloud has approximately 30 members, most of which are low luminosity dwarfs. The hot X-ray emitting gas is centered about halfway between NGC 4261 and NGC 4264 and extends out to a radius of approximately 40 min(620 kpc). The spectral data for the diffuse component are well fitted with a Raymond-Smith plasma model with a temperature of 0.85(sup +0.21)(sub -0.16) keV and abundance less than 0.08 times the solar value. Under the assumption that the diffuse gas is in hydrostatic equilibrium the total mass within 40 min is 1.9 x 10(exp 13) solar mass. We estimate that the total baryonic mass of the hot gas and the galaxies is 20%-34% of the total mass in the central 40 min radius of this group. This group of galaxies contains NGC 4273 which exhibits a 'bow shock' morphology similar to that of NGC 2276. This is thought to occur when the ram pressure from the intragroup gas significantly perturbs the interstellar medium in a late-type galaxy. We show that this is unlikely in this group.

Diffuse hot gas in the NGC 4261 group of galaxies

NASA Astrophysics Data System (ADS)

Davis, David S.; Mushotzky, Richard F.; Mulchaey, John S.; Worrall, D. M.; Birkinshaw, M.; Burstein, David

1995-05-01

We have found diffuse X-ray gas in the group of galaxies containing the elliptical galaxy NGC 4261. This galaxy along with its associated companions are behind the Virgo cluster in the W-cloud. A recent analysis of the velocity structure in the Virgo region indicates that the W-cloud has approximately 30 members, most of which are low luminosity dwarfs. The hot X-ray emitting gas is centered about halfway between NGC 4261 and NGC 4264 and extends out to a radius of approximately 40 min(620 kpc). The spectral data for the diffuse component are well fitted with a Raymond-Smith plasma model with a temperature of 0.85+0.21-0.16 keV and abundance less than 0.08 times the solar value. Under the assumption that the diffuse gas is in hydrostatic equilibrium the total mass within 40 min is 1.9 x 1013 solar mass. We estimate that the total baryonic mass of the hot gas and the galaxies is 20%-34% of the total mass in the central 40 min radius of this group. This group of galaxies contains NGC 4273 which exhibits a 'bow shock' morphology similar to that of NGC 2276. This is thought to occur when the ram pressure from the intragroup gas significantly perturbs the interstellar medium in a late-type galaxy. We show that this is unlikely in this group.

The formation of compact groups of galaxies. I: Optical properties

NASA Technical Reports Server (NTRS)

Diaferio, Antonaldo; Geller, Margaret J.; Ramella, Massimo

1994-01-01

The small crossing time of compact groups of galaxies (t(sub cr)H(sub 0) approximately less than 0.02) makes it hard to understand why they are observable at all. Our dissipationless N-body simulations show that within a single rich collapsing group compact groups of galaxies continually form. The mean lifetime of a particular compact configuration if approximately 1 Gyr. On this time scale, members may merge and/or other galaxies in the loose group may join the compact configuration. In other words, compact configurations are continually replaced by new systems. The frequency of this process explains the observability of compact groups. Our model produces compact configurations (compact groups (CG's) with optical properties remarkably similar to Hickson's (1982) compact groups (HCG's): (1) CG's have a frequency distribution of members similar to that of HCG's; (2) CG's are approximately equals 10 times as dense as loose groups; (3) CG's have dynamical properties remarkably similar to those of HCG's; (4) most of the galaxy members of CG's are not merger remnants. The crucial aspect of the model is the relationship between CG's and the surrounding rich loose group. Our model predicts the frequency of occurrence of CG's. A preliminary analysis of 18 rich loose groups is consistent with the model prediction. We suggest further observational tests of the model.

Dark energy in systems of galaxies

NASA Astrophysics Data System (ADS)

Chernin, A. D.

2013-11-01

The precise observational data of the Hubble Space Telescope have been used to study nearby galaxy systems. The main result is the detection of dark energy in groups, clusters, and flows of galaxies on a spatial scale of about 1-10 Mpc. The local density of dark energy in these systems, which is determined by various methods, is close to the global value or even coincides with it. A theoretical model of the nearby Universe has been constructed, which describes the Local Group of galaxies with the flow of dwarf galaxies receding from this system. The key physical parameter of the group-flow system is zero gravity radius, which is the distance at which the gravity of dark matter is compensated by dark-energy antigravity. The model predicts the existence of local regions of space where Einstein antigravity is stronger than Newton gravity. Six such regions have been revealed in the data of the Hubble space telescope. The nearest of these regions is at a distance of 1-3 Mpc from the center of the Milky Way. Antigravity in this region is several times stronger than gravity. Quasiregular flows of receding galaxies, which are accelerated by the dark-energy antigravity, exist in these regions. The model of the nearby Universe at the scale of groups of galaxies (˜1 Mpc) can be extended to the scale of clusters (˜10 Mpc). The systems of galaxies with accelerated receding flows constitute a new and probably widespread class of metagalactic populations. Strong dynamic effects of local dark energy constitute the main characteristic feature of these systems.

Fossil Groups in the Local Universe

NASA Technical Reports Server (NTRS)

OSullivan, Ewan

2005-01-01

The two galaxies observed as part of this project were originally selected as fossil group candidates because of their isolation from other galaxies and their apparent high X-ray luminosity and extended X-ray emission. However, the X-ray data available was minimal, being drawn from the ROSAT All-Sky Survey. We have performed an initial analysis of the XMM data from both galaxies and found that their gaseous halos are smaller, cooler, and less luminous than expected. In the case of NGC 57, the RASS estimate of extent and luminosity was biased because of a previously unidentified background group which is visible in the XMM data to one side of the galaxy. In the case of IC 153 1, the contribution from background point sources near the galaxy appears to be to blame. This suggests that both galaxies should be reclassified as isolated ellipticals. Such systems are very rare, and currently poorly understood; for comparison, there are now 6-10 known fossil groups, but only one isolated elliptical with useful X-ray data. We are currently re-analyzing the data for the two galaxies to take advantage of the calibration improvements of SAS 6.1, and to include calculations of the mass profiles of the two systems. A paper is currently in preparation dealing with the X-ray properties and environment of the galaxies, and we expect to submit this to the Astrophysical Journal within the next two months. Multi-band optical imaging of the field surrounding NGC 57 has been acquired to confirm its isolated status and provide more information on the background group. IC 1531 was accepted as a target in Chandra cycle 6 as part of a related proposal, and we intend to add this new observation to our XMM data when it becomes available. A second paper is planned to include the results of this combined analysis.

Constraining the Nature of Dark Matter with the Star-formation History of the Faintest Local Group Dwarf Galaxy Satellites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chau, Alice; Mayer, Lucio; Governato, Fabio

Λ warm dark matter (ΛWDM), realized by collisionless particles of 1–3 keV, has been proposed as an alternative scenario to Λ-Cold-Dark Matter (ΛCDM) for the dwarf galaxy scale discrepancies. We present an approach to test the viability of such WDM models using star-formation histories (SFHs) of the dwarf spheroidal galaxies (dSphs) in the Local Group. We compare their high-time-resolution SFHs with the collapse redshift of their dark halos in CDM and WDM. Collapse redshift is inferred after determining the subhalo infall mass. This is based on the dwarf current mass inferred from stellar kinematics, combined with cosmological simulation results onmore » subhalo evolution. WDM subhalos close to the filtering mass scale, forming significantly later than CDM, are the most difficult to reconcile with early truncation of star formation ( z ≥ 3). The ultra-faint dwarfs (UFDs) provide the most stringent constraints. Using six UFDs and eight classical dSphs, we show that a 1 keV particle is strongly disfavored, consistently with other reported methods. Excluding other models is only hinted for a few UFDs. Other UFDs for which the lack of robust constraints on halo mass prevents us from carrying out our analysis rigorously, show a very early onset of star formation that will strengthen the constraints delivered by our method in the future. We discuss the various caveats, notably the low number of dwarfs with accurately determined SFHs and the uncertainties when determining the subhalo infall mass, most notably the baryonic physics. Our preliminary analysis may serve as a pathfinder for future investigations that will combine accurate SFHs for local dwarfs with direct analysis of WDM simulations with baryons.« less

Characterising the Dense Molecular Gas in Exceptional Local Galaxies

NASA Astrophysics Data System (ADS)

Tunnard, Richard C. A.

2016-08-01

The interferometric facilities now coming online (the Atacama Large Millimetre Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA)) and those planned for the coming decade (the Next Generation Very Large Array (ngVLA) and the Square Kilometre Array (SKA)) in the radio to sub-millimetre regimes are opening a window to the molecular gas in high-redshift galaxies. However, our understanding of similar galaxies in the local universe is still far from complete and the data analysis techniques and tools needed to interpret the observations in consistent and comparable ways are yet to be developed. I first describe the Monte Carlo Markov Chain (MCMC) script developed to empower a public radiative transfer code. I characterise both the public code and MCMC script, including an exploration of the effect of observing molecular lines at high redshift where the Cosmic Microwave Background (CMB) can provide a significant background, as well as the effect this can have on well-known local correlations. I present two studies of ultraluminous infrared galaxies (ULIRGs) in the local universe making use of literature and collaborator data. In the first of these, NGC6240, I use the wealth of available data and the geometry of the source to develop a multi-phase, multi-species model, finding evidence for a complex medium of hot diffuse and cold dense gas in pressure equilibrium. Next, I study the prototypical ULIRG Arp 220; an extraordinary galaxy rendered especially interesting by the controversy over the power source of the western of the two merger nuclei and its immense luminosity and dust obscuration. Using traditional grid based methods I explore the molecular gas conditions within the nuclei and find evidence for chemical differentiation between the two nuclei, potentially related to the obscured power source. Finally, I investigate the potential evolution of proto-clusters over cosmic time with sub-millimetre observations of 14 radio galaxies, unexpectedly finding

Dust Evolution in Low-Metallicity Environments: Bridging the Gap Between Local Universe and Primordial Galaxies

NASA Astrophysics Data System (ADS)

Galliano, Frederic; Barlow, Mike; Bendo, George; Boselli, Alessandro; Buat, Veronique; Chanial, Pierre; Clements, David; Davies, Jon; Eales, Steve; Gomez, Haley; Isaak, Kate; Madden, Suzanne; Page, Mathew; Perez Fournon, Ismael; Sauvage, Marc; Spinoglio, Luigi; Vaccari, Mattia; Wilson, Christine

2008-03-01

The local galaxy Science Advisory Group (SAG 2) in the Herschel/SPIRE consortium, has constructed a Guaranteed Time Key Program using the PACS and SPIRE insruments to obtain 60 to 550 micron photometry of a statistically significant sample of 51 dwarf galaxies in our local universe chosen to cover an impressivly broad range of physical conditions. Here we propose the necessary complementary IRAC, MIPS and IRS Spitzer observations which together with the Herschel GT database will provide a rich database to the community to perform the dust and gas analyses in unprecedented detail in low metallicity galaxies ranging between 1/50 to 1 solar metallicity. Due to their chemical youth, and to the extreme conditions they experience, low metallicity environments constitute a keystone to understand dust evolution. The primary goal of this combined Herschel and Spitzer project is to study in details the physical processes at play within the ISM of these galaxies. We will take advantage of the powerful combination of Spitzer, Herschel and ancillary data to decompose the SED into the emission coming from the main phases of the ISM. Such a decomposition will provide reliable estimate of the abundances of the principal dust species, as a fonction of metallicity and physical conditions. These results will be exploited to compare the various evolutionary processes affecting the dust content of galaxies. All these outstanding scientific advances will be the true legacy value that this project brings to the community.

Stellar systems in the direction of the Hickson Compact Group 44. I. Low surface brightness galaxies

NASA Astrophysics Data System (ADS)

Smith Castelli, A. V.; Faifer, F. R.; Escudero, C. G.

2016-11-01

Context. In spite of the numerous studies of low-luminosity galaxies in different environments, there is still no consensus about their formation scenario. In particular, a large number of galaxies displaying extremely low-surface brightnesses have been detected in the last year, and the nature of these objects is under discussion. Aims: In this paper we report the detection of two extended low-surface brightness (LSB) objects (μeffg' ≃ 27 mag) found, in projection, next to NGC 3193 and in the zone of the Hickson Compact Group (HCG) 44, respectively. Methods: We analyzed deep, high-quality, GEMINI-GMOS images with ELLIPSE within IRAF in order to obtain their brightness profiles and structural parameters. We also searched for the presence of globular clusters (GC) in these fields. Results: We have found that, if these LSB galaxies were at the distances of NGC 3193 and HCG 44, they would show sizes and luminosities similar to those of the ultra-diffuse galaxies (UDGs) found in the Coma cluster and other associations. In that case, their sizes would be rather larger than those displayed by the Local Group dwarf spheroidal (dSph) galaxies. We have detected a few unresolved sources in the sky zone occupied by these galaxies showing colors and brightnesses typical of blue globular clusters. Conclusions: From the comparison of the properties of the galaxies presented in this work with those of similar objects reported in the literature, we have found that LSB galaxies display sizes covering a quite extended continous range (reff 0.3-4.5 kpc), in contrast to "normal" early-type galaxies, which show reff 1.0 kpc with a low dispersion. This fact might point to different formation processes for both types of galaxies.

FRESH ACTIVITY IN OLD SYSTEMS: RADIO AGNs IN FOSSIL GROUPS OF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hess, Kelley M.; Wilcots, Eric M.; Hartwick, Victoria L., E-mail: hess@ast.uct.ac.za, E-mail: ewilcots@astro.wisc.edu, E-mail: vhartwick@wisc.edu

2012-08-15

We present the first systematic 1.4 GHz Very Large Array radio continuum survey of fossil galaxy group candidates. These are virialized systems believed to have assembled over a gigayear in the past through the merging of galaxy group members into a single, isolated, massive elliptical galaxy and featuring an extended hot X-ray halo. We use new photometric and spectroscopic data from Sloan Digital Sky Survey Data Release 7 to determine that three of the candidates are clearly not fossil groups. Of the remaining 30 candidates, 67% contain a radio-loud (L{sub 1.4GHz} > 10{sup 23} W Hz{sup -1}) active galactic nucleusmore » (AGN) at the center of their dominant elliptical galaxy. We find a weak correlation between the radio luminosity of the AGN and the X-ray luminosity of the halo suggesting that the AGN contributes to energy deposition into the intragroup medium. We only find a correlation between the radio and optical luminosity of the central elliptical galaxy when we include X-ray-selected, elliptically dominated non-fossil groups, indicating a weak relationship between AGN strength and the mass assembly history of the groups. The dominant elliptical galaxy of fossil groups is on average roughly an order of magnitude more luminous than normal group elliptical galaxies in optical, X-ray, and radio luminosities and our findings are consistent with previous results that the radio-loud fraction in elliptical galaxies is linked to the stellar mass of a population. The current level of activity in fossil groups suggests that AGN fueling continues long after the last major merger. We discuss several possibilities for fueling the AGN at the present epoch.« less

Probing the Dusty Stellar Populations of the Local Volume Galaxies with JWST/MIRI

NASA Astrophysics Data System (ADS)

Jones, Olivia C.; Meixner, Margaret; Justtanont, Kay; Glasse, Alistair

2017-05-01

The Mid-Infrared Instrument (MIRI) for the James Webb Space Telescope (JWST) will revolutionize our understanding of infrared stellar populations in the Local Volume. Using the rich Spitzer-IRS spectroscopic data set and spectral classifications from the Surveying the Agents of Galaxy Evolution (SAGE)-Spectroscopic survey of more than 1000 objects in the Magellanic Clouds, the Grid of Red Supergiant and Asymptotic Giant Branch Star Model (grams), and the grid of YSO models by Robitaille et al., we calculate the expected flux densities and colors in the MIRI broadband filters for prominent infrared stellar populations. We use these fluxes to explore the JWST/MIRI colors and magnitudes for composite stellar population studies of Local Volume galaxies. MIRI color classification schemes are presented; these diagrams provide a powerful means of identifying young stellar objects, evolved stars, and extragalactic background galaxies in Local Volume galaxies with a high degree of confidence. Finally, we examine which filter combinations are best for selecting populations of sources based on their JWST colors.

Nucleosynthesis of intermediate mass stars: inferences from the observed abundances in photoionized nebulae of the Local Group

NASA Astrophysics Data System (ADS)

Maciel, W. J.; Costa, R. D. D.; Cavichia, O.

2018-01-01

Photoionized nebulae, comprising HII regions and planetary nebulae, are excellent laboratories to investigate the nucleosynthesis and chemical evolution of several elements in the Galaxy and other galaxies of the Local Group. Our purpose in this investigation is threefold: (i) to compare the abundances of HII regions and planetary nebulae in each system in order to investigate the differences derived from the age and origin of these objects, (ii) to compare the chemical evolution in different systems, such as the Milky Way, the Magellanic Clouds, and other galaxies of the Local Group, and (iii) to investigate to what extent the nucleosynthesis contributions from the progenitor stars affect the observed abundances in planetary nebulae, especially for oxygen and neon, which places constraints on the amount of these elements that can be produced by intermediate mass stars.

Galaxy NGC 55

NASA Technical Reports Server (NTRS)

2003-01-01

This image of the nearby edge-on spiral galaxy NGC 55 was taken by Galaxy Evolution Explorer on September 14, 2003, during 2 orbits. This galaxy lies 5.4 million light years from our Milky Way galaxy and is a member of the 'local group' of galaxies that also includes the Andromeda galaxy (M31), the Magellanic clouds, and 40 other galaxies. The spiral disk of NGC 55 is inclined to our line of sight by approximately 80 degrees and so this galaxy looks cigar-shaped. This picture is a combination of Galaxy Evolution Explorer images taken with the far ultraviolet (colored blue) and near ultraviolet detectors, (colored red). The bright blue regions in this image are areas of active star formation detected in the ultraviolet by Galaxy Evolution Explorer. The red stars in this image are foreground stars in our own Milky Way galaxy.

Evolution of the distribution of baryons in a simulated Local Group Universe

NASA Astrophysics Data System (ADS)

Peirani, S.

2012-12-01

Using hydrodynamical zoom simulations in the standard ΛCDM cosmology, we have investigated the evolution of the distribution of baryons (gas and stars) in a local group-type universe. We found that physical mechanisms able to drive the gas out of the virial radius at high redshifts (such as AGN) will have a stronger impact on the deficit of baryons in the mass budget of Milky Way type-galaxies at present times than those that expel the gas in the longer, late phases of galaxy formation.

DUST PROPERTIES OF LOCAL DUST-OBSCURED GALAXIES WITH THE SUBMILLIMETER ARRAY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hwang, Ho Seong; Andrews, Sean M.; Geller, Margaret J., E-mail: hhwang@cfa.harvard.edu, E-mail: sandrews@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu

We report Submillimeter Array observations of the 880 μm dust continuum emission for four dust-obscured galaxies (DOGs) in the local universe. Two DOGs are clearly detected with S{sub ν}(880 μm) =10-13 mJy and S/N > 5, but the other two are not detected with 3σ upper limits of S{sub ν}(880 μm) =5-9 mJy. Including an additional two local DOGs with submillimeter data from the literature, we determine the dust masses and temperatures for six local DOGs. The infrared luminosities and dust masses for these DOGs are in the ranges of 1.2-4.9 × 10{sup 11}(L{sub ☉}) and 4-14 × 10{sup 7}(M{submore » ☉}), respectively. The dust temperatures derived from a two-component modified blackbody function are 23-26 K and 60-124 K for the cold and warm dust components, respectively. Comparison of local DOGs with other infrared luminous galaxies with submillimeter detections shows that the dust temperatures and masses do not differ significantly among these objects. Thus, as argued previously, local DOGs are not a distinctive population among dusty galaxies, but simply represent the high-end tail of the dust obscuration distribution.« less

Luminous Infrared Sources in the Local Group: Identifying the Missing Links in Massive Star Evolution

NASA Astrophysics Data System (ADS)

Britavskiy, N.; Bonanos, A. Z.; Mehner, A.

2015-01-01

We present the first systematic survey of dusty massive stars (RSGs, LBVs, sgB[e]) in nearby galaxies, with the goal of understanding their importance in massive star evolution. Using the fact that these stars are bright in mid-infrared colors due to dust, we provide a technique for selecting and identifying dusty evolved stars based on the results of Bonanos et al. (2009, 2010), Britavskiy et al. (2014), and archival Spitzer/IRAC photometry. We present the results of our spectroscopic follow-up of luminous infrared sources in the Local Group dwarf irregular galaxies: Pegasus, Phoenix, Sextans A and WLM. The survey aims to complete the census of dusty massive stars in the Local Group.

The infrared luminosity function of AKARI 90 μm galaxies in the local Universe

NASA Astrophysics Data System (ADS)

Kilerci Eser, Ece; Goto, Tomotsugu

2018-03-01

Local infrared (IR) luminosity functions (LFs) are necessary benchmarks for high-redshift IR galaxy evolution studies. Any accurate IR LF evolution studies require accordingly accurate local IR LFs. We present IR galaxy LFs at redshifts of z ≤ 0.3 from AKARI space telescope, which performed an all-sky survey in six IR bands (9, 18, 65, 90, 140, and 160 μm) with 10 times better sensitivity than its precursor Infrared Astronomical Satellite. Availability of 160 μm filter is critically important in accurately measuring total IR luminosity of galaxies, covering across the peak of the dust emission. By combining data from Wide-field Infrared Survey Explorer (WISE), Sloan Digital Sky Survey (SDSS) Data Release 13 (DR 13), six-degree Field Galaxy Survey and the 2MASS Redshift Survey, we created a sample of 15 638 local IR galaxies with spectroscopic redshifts, factor of 7 larger compared to previously studied AKARI-SDSS sample. After carefully correcting for volume effects in both IR and optical, the obtained IR LFs agree well with previous studies, but comes with much smaller errors. Measured local IR luminosity density is ΩIR = 1.19 ± 0.05 × 108L⊙ Mpc-3. The contributions from luminous IR galaxies and ultraluminous IR galaxies to ΩIR are very small, 9.3 per cent and 0.9 per cent, respectively. There exists no future all-sky survey in far-IR wavelengths in the foreseeable future. The IR LFs obtained in this work will therefore remain an important benchmark for high-redshift studies for decades.

The Star Formation Demographics of Galaxies in the Local Volume

NASA Astrophysics Data System (ADS)

Lee, Janice C.; Kennicutt, Robert C.; Funes, S. J., José G.; Sakai, Shoko; Akiyama, Sanae

2007-12-01

We examine the connections between the current global star formation activity, luminosity, dynamical mass, and morphology of galaxies in the Local Volume, using Hα data from the 11 Mpc Hα and Ultraviolet Galaxy Survey (11HUGS). Taking the equivalent width (EW) of the Hα emission line as a tracer of the specific star formation rate, we analyze the distribution of galaxies in the MB-EW and rotational velocity (Vmax)-EW planes. Star-forming galaxies show two characteristic transitions in these planes. A narrowing of the galaxy locus occurs at MB~-15 and Vmax~50 km s-1, where the scatter in the logarithmic EWs drops by a factor of 2 as the luminosities/masses increase, and galaxy morphologies shift from predominately irregular to late-type spiral. Another transition occurs at MB~-19 and Vmax~120 km s-1, above which the sequence turns off toward lower EWs and becomes mostly populated by intermediate- and early-type bulge-prominent spirals. Between these two transitions, the mean logarithmic EW appears to remain constant at 30 Å. We comment on how these features reflect established empirical relationships, and provide clues for identifying the large-scale physical processes that both drive and regulate star formation, with emphasis on the low-mass galaxies which dominate our approximately volume-limited sample.

Galaxy NGC 55

NASA Image and Video Library

2003-12-10

This image of the nearby edge-on spiral galaxy NGC 55 was taken by Galaxy Evolution Explorer on September 14, 2003, during 2 orbits. This galaxy lies 5.4 million light years from our Milky Way galaxy and is a member of the "local group" of galaxies that also includes the Andromeda galaxy (M31), the Magellanic clouds, and 40 other galaxies. The spiral disk of NGC 55 is inclined to our line of sight by approximately 80 degrees and so this galaxy looks cigar-shaped. This picture is a combination of Galaxy Evolution Explorer images taken with the far ultraviolet (colored blue) and near ultraviolet detectors, (colored red). The bright blue regions in this image are areas of active star formation detected in the ultraviolet by Galaxy Evolution Explorer. The red stars in this image are foreground stars in our own Milky Way galaxy. http://photojournal.jpl.nasa.gov/catalog/PIA04923

Chemo-Dynamical Evolution of r-process Elements in the Local Group Galaxies

NASA Astrophysics Data System (ADS)

Hirai, Yutaka; Ishimaru, Yuhri; Saitoh, Takayuki R.; Fujii, Michiko S.; Hidaka, Jun; Kajino, Toshitaka

The astrophysical site(s) of r-process is not yet identified over half a century. Astronomical high dispersion observations have shown that extremely metal-poor (EMP) stars in the Milky Way (MW) halo have large star-to-star dispersions in the abundance of r-process elements. Binary neutron star mergers (NSMs) are one of the most promising sites of r-process. However, several studies suggested that it is difficult to reproduce the dispersions by NSMs due to their long merger times and low rates. In this study, we performed a series of N-body/smoothed particle hydrodynamic simulations of dwarf galaxies. We show that NSMs can explain the dispersions with long merger times (˜100 Myr). We find that the metallicity of our simulated galaxies does not correlate with time in their early phase due to slow chemical enrichment. This slow chemical enrichment produces [Eu/Fe] distribution which is consistent with the observation. Our results suggest that stars in the MW halo formed with a low star formation rate of less than 10 - 3M ⊙ yr-1, which is common for typical dwarf galaxies in the MW. Our simulations support the scenario that early enrichment of the MW halo occurred in the framework of hierarchical structure formation.

A model for the formation of the Local Group

NASA Technical Reports Server (NTRS)

Peebles, P. J. E.; Melott, A. L.; Holmes, M. R.; Jiang, L. R.

1989-01-01

Observational tests of a model for the formation of the Local Group are presented and analyzed in which the mass concentration grows by gravitational accretion of local-pressure matter onto two seed masses in an otherwise homogeneous initial mass distribution. The evolution of the mass distribution is studied in an analytic approximation and a numerical computation. The initial seed mass and separation are adjusted to produce the observed present separation and relative velocity of the Andromeda Nebula and the Galaxy. If H(0) is adjusted to about 80 km/s/Mpc with density parameter Omega = 1, then the model gives a good fit to the motions of the outer members of the Local Group. The same model gives particle orbits at radius of about 100 kpc that reasonably approximate the observed distribution of redshifts of the Galactic satellites.

Lost but not forgotten: intracluster light in galaxy groups and clusters

NASA Astrophysics Data System (ADS)

DeMaio, Tahlia; Gonzalez, Anthony H.; Zabludoff, Ann; Zaritsky, Dennis; Connor, Thomas; Donahue, Megan; Mulchaey, John S.

2018-03-01

With Hubble Space Telescope imaging, we investigate the progenitor population and formation mechanisms of the intracluster light (ICL) for 23 galaxy groups and clusters at 0.29 ≤ z ≤ 0.89. The colour gradients of the BCG+ICL become bluer with increasing radius out to 53-100 kpc for all but one system, suggesting that violent relaxation after major mergers with the BCG cannot be the dominant source of ICL. The BCG+ICL luminosities and stellar masses are too large for the ICL stars to come from the dissolution of dwarf galaxies alone, given the observed evolution of the faint end of the cluster galaxy luminosity function, implying instead that the ICL grows from the stripping of more massive galaxies. Using the colours of cluster members from the CLASH high-mass sample, we place conservative lower limits on the luminosities of galaxies from which the ICL at r < 100 kpc could originate via stripping. We find that the ICL at 100 kpc has a colour similar to a 1010.0 M⊙ galaxy and that 75 per cent of the total BCG+ICL luminosity at r < 100 kpc is consistent with originating in galaxies with L > 0.2 L* (log(M★ [M⊙])>10.4), assuming conservatively that these galaxies are completely disrupted. We conclude that the tidal stripping of massive galaxies is the likely source of the intracluster light from 10 to 100 kpc for galaxy groups and clusters.

The Ultraviolet and Infrared Star Formation Rates of Compact Group Galaxies: An Expanded Sample

NASA Technical Reports Server (NTRS)

Lenkic, Laura; Tzanavaris, Panayiotis; Gallagher, Sarah C.; Desjardins, Tyler D.; Walker, Lisa May; Johnson, Kelsey E.; Fedotov, Konstantin; Charlton, Jane; Cardiff, Ann H.; Durell, Pat R.

2016-01-01

Compact groups of galaxies provide insight into the role of low-mass, dense environments in galaxy evolution because the low velocity dispersions and close proximity of galaxy members result in frequent interactions that take place over extended time-scales. We expand the census of star formation in compact group galaxies by Tzanavaris et al. (2010) and collaborators with Swift UVOT, Spitzer IRAC and MIPS 24 m photometry of a sample of 183 galaxies in 46 compact groups. After correcting luminosities for the contribution from old stellar populations, we estimate the dust-unobscured star formation rate (SFRUV) using the UVOT uvw2 photometry. Similarly, we use the MIPS 24 m photometry to estimate the component of the SFR that is obscured by dust (SFRIR). We find that galaxies which are MIR-active (MIR-red), also have bluer UV colours, higher specific SFRs, and tend to lie in Hi-rich groups, while galaxies that are MIR-inactive (MIR-blue) have redder UV colours, lower specific SFRs, and tend to lie in Hi-poor groups. We find the SFRs to be continuously distributed with a peak at about 1 M yr1, indicating this might be the most common value in compact groups. In contrast, the specific SFR distribution is bimodal, and there is a clear distinction between star-forming and quiescent galaxies. Overall, our results suggest that the specific SFR is the best tracer of gas depletion and galaxy evolution in compact groups.

INTRAGROUP AND GALAXY-LINKED DIFFUSE X-RAY EMISSION IN HICKSON COMPACT GROUPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Desjardins, Tyler D.; Gallagher, Sarah C.; Tzanavaris, Panayiotis

2013-02-15

Isolated compact groups (CGs) of galaxies present a range of dynamical states, group velocity dispersions, and galaxy morphologies with which to study galaxy evolution, particularly the properties of gas both within the galaxies and in the intragroup medium. As part of a large, multiwavelength examination of CGs, we present an archival study of diffuse X-ray emission in a subset of nine Hickson compact groups (HCGs) observed with the Chandra X-Ray Observatory. We find that seven of the groups in our sample exhibit detectable diffuse emission. However, unlike large-scale emission in galaxy clusters, the diffuse features in the majority of themore » detected groups are linked to the individual galaxies, in the form of both plumes and halos likely as a result of vigourous star formation or activity in the galaxy nucleus, as well as in emission from tidal features. Unlike previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found to be consistent with the L{sub X} -T relationship from clusters within the errors, while HCGs 16 and 31 are consistent with the cluster L{sub X} -{sigma} relation, though this is likely coincidental given that the hot gas in these two systems is largely due to star formation. We find that L{sub X} increases with decreasing group H I to dynamical-mass ratio with tentative evidence for a dependence in X-ray luminosity on H I morphology whereby systems with intragroup H I indicative of strong interactions are considerably more X-ray luminous than passively evolving groups. We also find a gap in the L{sub X} of groups as a function of the total group specific star formation rate. Our findings suggest that the hot gas in these groups is not in hydrostatic equilibrium and these systems are not low-mass analogs of rich groups or clusters, with the possible exception of HCG 62.« less

Intragroup and Galaxy-linked Diffuse X-ray Emission In Hickson Compact Groups

NASA Technical Reports Server (NTRS)

Desjardins, Tyler D.; Gallagher, Sarah C.; Tzanavaris, Panayiotis; Mulchaey, John S.; Brandt, William N.; Charlton, Jane C.; Garmire, Gordon P.; Gronwall, Caryl; Cardiff, Ann; Johnson, Kelsey E.;

Probing the Dusty Stellar Populations of the Local Volume Galaxies with JWST /MIRI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, Olivia C.; Meixner, Margaret; Justtanont, Kay

The Mid-Infrared Instrument (MIRI) for the James Webb Space Telescope ( JWST ) will revolutionize our understanding of infrared stellar populations in the Local Volume. Using the rich Spitzer -IRS spectroscopic data set and spectral classifications from the Surveying the Agents of Galaxy Evolution (SAGE)–Spectroscopic survey of more than 1000 objects in the Magellanic Clouds, the Grid of Red Supergiant and Asymptotic Giant Branch Star Model (grams), and the grid of YSO models by Robitaille et al., we calculate the expected flux densities and colors in the MIRI broadband filters for prominent infrared stellar populations. We use these fluxes tomore » explore the JWST /MIRI colors and magnitudes for composite stellar population studies of Local Volume galaxies. MIRI color classification schemes are presented; these diagrams provide a powerful means of identifying young stellar objects, evolved stars, and extragalactic background galaxies in Local Volume galaxies with a high degree of confidence. Finally, we examine which filter combinations are best for selecting populations of sources based on their JWST colors.« less

The Undergraduate ALFALFA Groups Project: Properties of the Galaxy Group MKW 11

NASA Astrophysics Data System (ADS)

Manglitz, Scott; Russell, P.; Turner, J.; Crone, M.

2009-01-01

The Undergraduate ALFALFA team is an NSF-funded collaboration of 14 institutions that supports undergraduate research using data from the Arecibo Legacy Fast ALFA (ALFALFA) survey. As part of this project, we are examining MKW 11, a galaxy group with an unusual, irregular X-ray distribution centered on what appears to be an X-ray bright tidal filament. Its optical velocity distribution is large and non-Gaussian, suggesting that it is in the process of merging. Here we present the position and velocity structure of MKW 11 using the radio sources in the blind ALFALFA survey. Besides a complicated structure, our results suggest a deficiency of HI gas in galaxies that are near the center of the group.

Cosmic Dawn (CoDa): the First Radiation-Hydrodynamics Simulation of Reionization and Galaxy Formation in the Local Universe

NASA Astrophysics Data System (ADS)

Ocvirk, Pierre; Gillet, Nicolas; Shapiro, Paul R.; Aubert, Dominique; Iliev, Ilian T.; Teyssier, Romain; Yepes, Gustavo; Choi, Jun-Hwan; Sullivan, David; Knebe, Alexander; Gottlöber, Stefan; D'Aloisio, Anson; Park, Hyunbae; Hoffman, Yehuda; Stranex, Timothy

2016-12-01

Cosmic reionization by starlight from early galaxies affected their evolution, thereby impacting reionization itself. Star formation suppression, for example, may explain the observed underabundance of Local Group dwarfs relative to N-body predictions for cold dark matter. Reionization modelling requires simulating volumes large enough [˜ (100 Mpc)3] to sample reionization `patchiness', while resolving millions of galaxy sources above ˜108 M⊙ combining gravitational and gas dynamics with radiative transfer. Modelling the Local Group requires initial cosmological density fluctuations pre-selected to form the well-known structures of the Local Universe today. Cosmic Dawn (`CoDa') is the first such fully coupled, radiation-hydrodynamics simulation of reionization of the Local Universe. Our new hybrid CPU-GPU code, RAMSES-CUDATON, performs hundreds of radiative transfer and ionization rate-solver timesteps on the GPUs for each hydro-gravity timestep on the CPUs. CoDa simulated (91Mpc)3 with 40963 particles and cells, to redshift 4.23, on ORNL supercomputer Titan, utilizing 8192 cores and 8192 GPUs. Global reionization ended slightly later than observed. However, a simple temporal rescaling which brings the evolution of ionized fraction into agreement with observations also reconciles ionizing flux density, cosmic star formation history, CMB electron scattering optical depth and galaxy UV luminosity function with their observed values. Photoionization heating suppressed the star formation of haloes below ˜2 × 109 M⊙, decreasing the abundance of faint galaxies around MAB1600 = [-10, -12]. For most of reionization, star formation was dominated by haloes between 1010-1011 M⊙ , so low-mass halo suppression was not reflected by a distinct feature in the global star formation history. Intergalactic filaments display sheathed structures, with hot envelopes surrounding cooler cores, but do not self-shield, unlike regions denser than 100 <ρ>.

Connecting the First Galaxies with Ultrafaint Dwarfs in the Local Group: Chemical Signatures of Population III Stars

NASA Astrophysics Data System (ADS)

Jeon, Myoungwon; Besla, Gurtina; Bromm, Volker

2017-10-01

We investigate the star formation history (SFH) and chemical evolution of isolated analogs of Local Group (LG) ultrafaint dwarf galaxies (UFDs; stellar mass range of {10}2 {M}⊙ < {M}* < {10}5 {M}⊙ ) and gas-rich, low-mass dwarfs (Leo P analogs; stellar mass range of {10}5 {M}⊙ < {M}* < {10}6 {M}⊙ ). We perform a suite of cosmological hydrodynamic zoom-in simulations to follow their evolution from the era of the first generation of stars down to z = 0. We confirm that reionization, combined with supernova (SN) feedback, is primarily responsible for the truncated star formation in UFDs. Specifically, halos with a virial mass of {M}{vir}≲ 2× {10}9 {M}⊙ form ≳ 90 % of stars prior to reionization. Our work further demonstrates the importance of Population III stars, with their intrinsically high [{{C}}/{Fe}] yields and the associated external metal enrichment, in producing low-metallicity stars ([{Fe}/{{H}}]≲ -4) and carbon-enhanced metal-poor (CEMP) stars. We find that UFDs are composite systems, assembled from multiple progenitor halos, some of which hosted only Population II stars formed in environments externally enriched by SNe in neighboring halos, naturally producing extremely low metallicity Population II stars. We illustrate how the simulated chemical enrichment may be used to constrain the SFHs of true observed UFDs. We find that Leo P analogs can form in halos with {M}{vir}˜ 4× {10}9 {M}⊙ (z = 0). Such systems are less affected by reionization and continue to form stars until z = 0, causing higher-metallicity tails. Finally, we predict the existence of extremely low metallicity stars in LG UFD galaxies that preserve the pure chemical signatures of Population III nucleosynthesis.

A search for extended radio emission from selected compact galaxy groups

NASA Astrophysics Data System (ADS)

Nikiel-Wroczyński, B.; Urbanik, M.; Soida, M.; Beck, R.; Bomans, D. J.

2017-07-01

Context. Studies on compact galaxy groups have led to the conclusion that a plenitude of phenomena take place in between galaxies that form them. However, radio data on these objects are extremely scarce and not much is known concerning the existence and role of the magnetic field in intergalactic space. Aims: We aim to study a small sample of galaxy groups that look promising as possible sources of intergalactic magnetic fields; for example data from radio surveys suggest that most of the radio emission is due to extended, diffuse structures in and out of the galaxies. Methods: We used the Effelsberg 100 m radio telescope at 4.85 GHz and NRAO VLA Sky Survey (NVSS) data at 1.40 GHz. After subtraction of compact sources we analysed the maps searching for diffuse, intergalactic radio emission. Spectral index and magnetic field properties were derived. Results: Intergalactic magnetic fields exist in groups HCG 15 and HCG 60, whereas there are no signs of them in HCG 68. There are also hints of an intergalactic bridge in HCG 44 at 4.85 GHz. Conclusions: Intergalactic magnetic fields exist in galaxy groups and their energy density may be comparable to the thermal (X-ray) density, suggesting an important role of the magnetic field in the intra-group medium, wherever it is detected.

The role of molecular gas in galaxy transition in compact groups

NASA Astrophysics Data System (ADS)

Lisenfeld, U.; Alatalo, K.; Zucker, C.; Appleton, P. N.; Gallagher, S.; Guillard, P.; Johnson, K.

2017-11-01

Compact groups (CGs) provide an environment in which interactions between galaxies and with the intra-group medium enable and accelerate galaxy transitions from actively star forming to quiescent. Galaxies in transition from active to quiescent can be selected, by their infrared (IR) colors, as canyon or infrared transition zone (IRTZ) galaxies. We used a sample of CG galaxies with IR data from the Wide Field Infrared Survey Explorer (WISE) allowing us to calculate the stellar mass and star formation rate (SFR) for each galaxy. Furthermore, we present new CO(1-0) data for 27 galaxies and collect data from the literature to calculate the molecular gas mass for a total sample of 130 galaxies. This data set allows us to study the difference in the molecular gas fraction (Mmol/M∗) and star formation efficiency (SFE = SFR/Mmol) between active, quiescent, and transitioning (I.e., canyon and IRTZ) galaxies. We find that transitioning galaxies have a mean molecular gas fraction and a mean SFE that are significantly lower than those of actively star-forming galaxies. The molecular gas fraction is higher than that of quiescent galaxies, whereas the SFE is similar. These results indicate that the transition from actively star-forming to quiescent in CG galaxies goes along with a loss of molecular gas, possibly due to tidal forces exerted from the neighboring galaxies or a decrease in the gas density. In addition, the remaining molecular gas loses its ability to form stars efficiently, possibly owing to turbulence perturbing the gas,as seen in other, well-studied examples such as Stephan's Quintet and HCG 57. Thus, the amount and properties of molecular gas play a crucial role in the environmentally driven transition of galaxies from actively star forming to quiescent. Full Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A110

Most Distant Group of Galaxies Known in the Universe

NASA Astrophysics Data System (ADS)

2002-04-01

New VLT Discovery Pushes Back the Beginnings Summary Using the ESO Very Large Telescope (VLT) , a team of astronomers from The Netherlands, Germany, France and the USA [1] have discovered the most distant group of galaxies ever seen , about 13.5 billion light-years away. It has taken the light now recorded by the VLT about nine-tenths of the age of the Universe to cover the huge distance. We therefore observe those galaxies as they were at a time when the Universe was only about 10% of its present age . The astronomers conclude that this group of early galaxies will develop into a rich cluster of galaxies, such as those seen in the nearby Universe. The newly discovered structure provides the best opportunity so far for studying when and how galaxies began to form clusters after the initial Big Bang , one of the greatest puzzles in modern cosmology. PR Photo 11a/02 : Sky field with the distant cluster of galaxies. PR Photo 11b/02 : Spectra of some of the galaxies in the cluster. Radio Galaxies as cosmic signposts A most intriguing question in modern astronomy is how the first groupings or "clusters" of galaxies emerged from the gas produced in the Big Bang. Some theoretical models predict that densely populated galaxy clusters ("rich clusters" in current astronomical terminology) are built up through a step-wise process. Clumps develop in the primeval gas, and stars condense out of these clumps to form small galaxies. Then these small galaxies merge together to form larger units. The peculiar class of "radio galaxies" is particularly important for investigating such scenarios. They are called so because their radio emission - a result of violent processes believed to be related to massive black holes located at the centres of these galaxies - is stronger by 5 - 10 orders of magnitude than that of our own Milky Way galaxy. In fact, this radio emission is often so intense that the galaxies can be spotted at extremely large distances, and thus at the remote epoch when

Hot and Cold Galactic Gas in the NGC 2563 Galaxy Group

NASA Astrophysics Data System (ADS)

Rasmussen, Jesper; Bai, Xue-Ning; Mulchaey, John S.; van Gorkom, J. H.; Jeltema, Tesla E.; Zabludoff, Ann I.; Wilcots, Eric; Martini, Paul; Lee, Duane; Roberts, Timothy P.

2012-03-01

The role of environmentally induced gas stripping in driving galaxy evolution in groups remains poorly understood. Here we present extensive Chandra and Very Large Array mosaic observations of the hot and cold interstellar medium within the members of the nearby, X-ray bright NGC 2563 group, a prime target for studies of the role of gas stripping and interactions in relatively small host halos. Our observations cover nearly all group members within a projected radius of 1.15 Mpc (~1.4 R vir) of the group center, down to a limiting X-ray luminosity and H I mass of 3 × 1039 erg s-1 and 2 × 108 M ⊙, respectively. The X-ray data are consistent with efficient ram pressure stripping of the hot gas halos of early-type galaxies near the group core, but no X-ray tails are seen and the limited statistics preclude strong conclusions. The H I results suggest moderate H I mass loss from the group members when compared to similar field galaxies. Six of the 20 H I-detected group members show H I evidence of ongoing interactions with other galaxies or with the intragroup medium. Suggestive evidence is further seen for galaxies with close neighbors in position-velocity space to show relatively low H I content, consistent with tidal removal of H I. The results thus indicate removal of both hot and cold gas from the group members via a combination of ram pressure stripping and tidal interactions. We also find that 16 of the 20 H I detections occur on one side of the group, reflecting an unusual morphological segregation whose origin remains unclear.

Suites of dwarfs around Nearby giant galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karachentsev, Igor D.; Kaisina, Elena I.; Makarov, Dmitry I., E-mail: ikar@sao.ru, E-mail: kei@sao.ru, E-mail: dim@sao.ru

2014-01-01

The Updated Nearby Galaxy Catalog (UNGC) contains the most comprehensive summary of distances, radial velocities, and luminosities for 800 galaxies located within 11 Mpc from us. The high density of observables in the UNGC makes this sample indispensable for checking results of N-body simulations of cosmic structures on a ∼1 Mpc scale. The environment of each galaxy in the UNGC was characterized by a tidal index Θ{sub 1}, depending on the separation and mass of the galaxy's main disturber (MD). We grouped UNGC galaxies with a common MD in suites, and ranked suite members according to their Θ{sub 1}. Allmore » suite members with positive Θ{sub 1} are assumed to be physical companions of the MD. About 58% of the sample are members of physical groups. The distribution of suites by the number of members, n, follows a relation N(n) ∼ n {sup –2}. The 20 most populated suites contain 468 galaxies, i.e., 59% of the UNGC sample. The fraction of MDs among the brightest galaxies is almost 100% and drops to 50% at M{sub B} = –18{sup m}. We discuss various properties of MDs, as well as galaxies belonging to their suites. The suite abundance practically does not depend on the morphological type, linear diameter, or hydrogen mass of the MD, the tightest correlation being with the MD dynamical mass. Dwarf galaxies around MDs exhibit well-known segregation effects: the population of the outskirts has later morphological types, richer H I contents, and higher rates of star formation activity. Nevertheless, there are some intriguing cases where dwarf spheroidal galaxies occur at the far periphery of the suites, as well as some late-type dwarfs residing close to MDs. Comparing simulation results with galaxy groups, most studies assume the Local Group is fairly typical. However, we recognize that the nearby groups significantly differ from each other and there is considerable variation in their properties. The suites of companions around the Milky Way and M31, consisting

Precision Scaling Relations for Disk Galaxies in the Local Universe

NASA Astrophysics Data System (ADS)

Lapi, A.; Salucci, P.; Danese, L.

2018-05-01

We build templates of rotation curves as a function of the I-band luminosity via the mass modeling (by the sum of a thin exponential disk and a cored halo profile) of suitably normalized, stacked data from wide samples of local spiral galaxies. We then exploit such templates to determine fundamental stellar and halo properties for a sample of about 550 local disk-dominated galaxies with high-quality measurements of the optical radius R opt and of the corresponding rotation velocity V opt. Specifically, we determine the stellar M ⋆ and halo M H masses, the halo size R H and velocity scale V H, and the specific angular momenta of the stellar j ⋆ and dark matter j H components. We derive global scaling relationships involving such stellar and halo properties both for the individual galaxies in our sample and for their mean within bins; the latter are found to be in pleasing agreement with previous determinations by independent methods (e.g., abundance matching techniques, weak-lensing observations, and individual rotation curve modeling). Remarkably, the size of our sample and the robustness of our statistical approach allow us to attain an unprecedented level of precision over an extended range of mass and velocity scales, with 1σ dispersion around the mean relationships of less than 0.1 dex. We thus set new standard local relationships that must be reproduced by detailed physical models, which offer a basis for improving the subgrid recipes in numerical simulations, that provide a benchmark to gauge independent observations and check for systematics, and that constitute a basic step toward the future exploitation of the spiral galaxy population as a cosmological probe.

A 17-billion-solar-mass black hole in a group galaxy with a diffuse core.

PubMed

Thomas, Jens; Ma, Chung-Pei; McConnell, Nicholas J; Greene, Jenny E; Blakeslee, John P; Janish, Ryan

2016-04-21

Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago. Two possible present-day 'dormant' descendants of this population of 'active' black holes have been found in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall--the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600--a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes.

Redshift-space distortions of group and galaxy correlations in the Updated Zwicky Catalog

NASA Astrophysics Data System (ADS)

Padilla, N. D.; Merchán, M.; García Lambas, D.; Maia, M. G.

We calculate two-point correlation functions of galaxies and groups of galaxies selected in three dimensions from the Updated Zwicky Galaxy Catalog - (UZC). The redshift space distortion of the correlation function ξ(σ,π) in the directions parallel and perpendicular to the line of sight, induced by pairwise group peculiar velocities is evaluated. Two methods are used to characterize the pairwise velocity field. The first method consists in fitting the observed ξ(σ,π) with a distorted model with an exponential pairwise velocity distribution, in fixed σ bins. The second method compares the contours of constant predicted correlation function of this model with the data. The results are consistent with a one-dimensional pairwise rms velocity dispersion of groups 1/2=250 ± 110 km/s. We find that UZC galaxy pairwise velocity dispersion is 1/2 = 460 ± 35 km/s. Such findings point towards a smoothly varying peculiar velocity field from galaxies to systems of galaxies, a expected in a hierarchical scenario of structure formation. We estimate the real-space correlation function in the power-law approximation ξ(r)=(r/r0)γ for groups and galaxies in UZC. We obtain the correlation length, r0, from the projected correlation function W(σ)=∫- ∞∞ξ(σ,π)dπ= 2 ∫0∞ ξ(σ,π) dπ using the values of γ derived from the correlation function in projected separations ω(σ). The best fitting parameters are γ=-1.89 ± 0.17 and r0=9.7 ± 4.5 Mpc h-1 for groups, and γ=-2.00 ± 0.03, r0=5.29 ± 0.21 Mpc h-1 for galaxies. We carried out an estimate of the parameter β= Ω0.6/b for groups and galaxies using the linear approximation regime relating the real and the redshift-space correlation functions. We find βgalaxies=0.51 ± 0.15 for galaxies, in agreement with previous works, while for groups we obtain a noisy estimate β < 1.5. We have tested our methods on mock UZC catalogs taken from N-body simulations. The results of these tests show that the

THE RELATION BETWEEN GALAXY MORPHOLOGY AND ENVIRONMENT IN THE LOCAL UNIVERSE: AN RC3-SDSS PICTURE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilman, David J.; Erwin, Peter

2012-02-20

We present results of an analysis of the local (z {approx} 0) morphology-environment relation for 911 bright (M{sub B} < -19) galaxies, based on matching classical RC3 morphologies with the Sloan Digital Sky Survey based group catalog of Yang et al., which includes halo mass estimates. This allows us to study how the relative fractions of spirals, lenticulars, and ellipticals depend on halo mass over a range of 10{sup 11.7}-10{sup 14.8} h{sup -1} M{sub Sun }, from isolated single-galaxy halos to massive groups and low-mass clusters. We pay particular attention to how morphology relates to central versus satellite status (wheremore » 'central' galaxies are the most massive within their halo). The fraction of galaxies which are elliptical is a strong function of stellar mass; it is also a strong function of halo mass, but only for central galaxies. We interpret this as evidence for a scenario where elliptical galaxies are always formed, probably via mergers, as central galaxies within their halos, with satellite ellipticals being previously central galaxies accreted onto a larger halo. The overall fraction of galaxies which are S0 increases strongly with halo mass, from {approx}10% to {approx}70%. Here, too, we find striking differences between the central and satellite populations. 20% {+-} 2% of central galaxies with stellar masses M{sub *} > 10{sup 10.5} M{sub Sun} are S0 regardless of halo mass, but satellite S0 galaxies are only found in massive (>10{sup 13} h{sup -1} M{sub Sun }) halos, where they are 69% {+-} 4% of the M{sub *} > 10{sup 10.5} M{sub Sun} satellite population. This suggests two channels for forming S0 galaxies: one which operates for central galaxies and another which transforms lower-mass (M{sub *} {approx}< 10{sup 11} M{sub Sun }) accreted spirals into satellite S0 galaxies in massive halos. Analysis of finer morphological structure (bars and rings in disk galaxies) shows some trends with stellar mass, but none with halo mass; this is

WINGS-SPE. III. Equivalent width measurements, spectral properties, and evolution of local cluster galaxies

NASA Astrophysics Data System (ADS)

Fritz, J.; Poggianti, B. M.; Cava, A.; Moretti, A.; Varela, J.; Bettoni, D.; Couch, W. J.; D'Onofrio D'Onofrio, M.; Dressler, A.; Fasano, G.; Kjærgaard, P.; Marziani, P.; Moles, M.; Omizzolo, A.

2014-06-01

Context. Cluster galaxies are the ideal sites to look at when studying the influence of the environment on the various aspects of the evolution of galaxies, such as the changes in their stellar content and morphological transformations. In the framework of wings, the WIde-field Nearby Galaxy-cluster Survey, we have obtained optical spectra for ~6000 galaxies selected in fields centred on 48 local (0.04 < z < 0.07) X-ray selected clusters to tackle these issues. Aims: By classifying the spectra based on given spectral lines, we investigate the frequency of the various spectral types as a function of both the clusters' properties and the galaxies' characteristics. In this way, using the same classification criteria adopted for studies at higher redshift, we can consistently compare the properties of the local cluster population to those of their more distant counterparts. Methods: We describe a method that we have developed to automatically measure the equivalent width of spectral lines in a robust way, even in spectra with a non optimal signal-to-noise ratio. This way, we can derive a spectral classification reflecting the stellar content, based on the presence and strength of the [Oii] and Hδ lines. Results: After a quality check, we are able to measure 4381 of the ~6000 originally observed spectra in the fields of 48 clusters, of which 2744 are spectroscopically confirmed cluster members. The spectral classification is then analysed as a function of galaxies' luminosity, stellar mass, morphology, local density, and host cluster's global properties and compared to higher redshift samples (MORPHS and EDisCS). The vast majority of galaxies in the local clusters population are passive objects, being also the most luminous and massive. At a magnitude limit of MV < -18, galaxies in a post-starburst phase represent only ~11% of the cluster population, and this fraction is reduced to ~5% at MV < -19.5, which compares to the 18% at the same magnitude limit for high

NGC 741—Mergers and AGN Feedback on a Galaxy-group Scale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schellenberger, G.; Vrtilek, J. M.; David, L.

Low-mass galaxy cluster systems and groups will play an essential role in upcoming cosmological studies, such as those to be carried out with eROSITA. Though the effects of active galactic nuclei (AGNs) and merging processes are of special importance to quantify biases like selection effects or deviations from hydrostatic equilibrium, they are poorly understood on the galaxy-group scale. We present an analysis of recent deep Chandra and XMM-Newton integrations of NGC 741 that provides an excellent example of a group with multiple concurrent phenomena: both an old central radio galaxy and a spectacular infalling head-tail source, strongly bent jets, amore » 100-kpc radio trail, intriguing narrow X-ray filaments, and gas-sloshing features. Supported principally by X-ray and radio continuum data, we address the merging history of the group, the nature of the X-ray filaments, the extent of gas-stripping from NGC 742, the character of cavities in the group, and the roles of the central AGN and infalling galaxy in heating the intra-group medium.« less

The frequency and properties of young tidal dwarf galaxies in nearby groups

NASA Astrophysics Data System (ADS)

Lee-Waddell, K.; Spekkens, K.; Chandra, P.; Patra, N.; Cuillandre, J.-C.; Wang, J.; Haynes, M. P.; Cannon, J.; Stierwalt, S.; Sick, J.; Giovanelli, R.

2017-03-01

We present the results of a multi-wavelength investigation of the dwarf galaxy populations in three interacting galaxy groups: NGC 871/6/7, NGC 3166/9, NGC 4725/47. Using degree-scale Giant Metrewave Radio Telescope Hi mosaics and deep optical photometry from the Canada-France-Hawaii Telescope, we measured the Hi and stellar properties of the gas-rich low-mass group members to classify each one as a classical dwarf galaxy, a short-lived tidal knot or a tidal dwarf galaxy (TDG). Our observations detect several dwarf irregulars and various tidal knots. We identify four potentially long-lived tidal objects in the three groups, implying that TDGs are not readily produced. The tidal objects examined in this small survey also appear to have a wider variety of properties than TDGs formed in current simulations.

Star Formation Histories of Dwarf Irregular Galaxies

NASA Astrophysics Data System (ADS)

Skillman, Evan

1995-07-01

We propose to obtain deep WFPC2 `BVI' color-magnitude diagrams {CMDs} for the dwarf irregular {dI} Local Group galaxies GR 8, Leo A, Pegasus, and Sextans A. In addition to resolved stars, we will use star clusters, and especially any globulars, to probe the history of intense star formation. These data will allow us to map the Pop I and Pop II stellar components, and thereby construct the first detailed star formation histories for non-interacting dI galaxies. Our results will bear on a variety of astrophysical problems, including the evolution of small galaxies, distances in the Local Group, age-metallicity distributions in small galaxies, ages of dIs, and the physics of star formation. The four target galaxies are typical dI systems in terms of luminosity, gas content, and H II region abundance, and represent a range in current star forming activity. They are sufficiently near to allow us to reach to stars at M_V = 0, have 0.1 of the luminosity of the SMC and 0.25 of its oxygen abundance. Unlike the SMC, these dIs are not near giant galaxies. This project will allow the extension of our knowledge of stellar populations in star forming galaxies from the spirals in the Local Group down to its smallest members. We plan to take maximum advantage of the unique data which this project will provide. Our investigator team brings extensive and varied experience in studies of dwarf galaxies, stellar populations, imaging photometry, and stellar evolution to this project.

A KiDS weak lensing analysis of assembly bias in GAMA galaxy groups

NASA Astrophysics Data System (ADS)

Dvornik, Andrej; Cacciato, Marcello; Kuijken, Konrad; Viola, Massimo; Hoekstra, Henk; Nakajima, Reiko; van Uitert, Edo; Brouwer, Margot; Choi, Ami; Erben, Thomas; Fenech Conti, Ian; Farrow, Daniel J.; Herbonnet, Ricardo; Heymans, Catherine; Hildebrandt, Hendrik; Hopkins, Andrew M.; McFarland, John; Norberg, Peder; Schneider, Peter; Sifón, Cristóbal; Valentijn, Edwin; Wang, Lingyu

2017-07-01

We investigate possible signatures of halo assembly bias for spectroscopically selected galaxy groups from the Galaxy And Mass Assembly (GAMA) survey using weak lensing measurements from the spatially overlapping regions of the deeper, high-imaging-quality photometric Kilo-Degree Survey. We use GAMA groups with an apparent richness larger than 4 to identify samples with comparable mean host halo masses but with a different radial distribution of satellite galaxies, which is a proxy for the formation time of the haloes. We measure the weak lensing signal for groups with a steeper than average and with a shallower than average satellite distribution and find no sign of halo assembly bias, with the bias ratio of 0.85^{+0.37}_{-0.25}, which is consistent with the Λ cold dark matter prediction. Our galaxy groups have typical masses of 1013 M⊙ h-1, naturally complementing previous studies of halo assembly bias on galaxy cluster scales.

The Flow-field From Galaxy Groups In 2MASS

NASA Astrophysics Data System (ADS)

Crook, Aidan; Huchra, J.; Macri, L.; Masters, K.; Jarrett, T.

2011-01-01

We present the first model of a flow-field in the nearby Universe (cz < 12,000 km/s) constructed from groups of galaxies identified in an all-sky flux-limited survey. The Two Micron All-Sky Redshift Survey (2MRS), upon which the model is based, represents the most complete survey of its class and, with near-IR fluxes, provides the optimal method for tracing baryonic matter in the nearby Universe. Peculiar velocities are reconstructed self-consistently with a density-field based upon groups identified in the 2MRS Ks<11.75 catalog. The model predicts infall toward Virgo, Perseus-Pisces, Hydra-Centaurus, Norma, Coma, Shapley and Hercules, and most notably predicts backside-infall into the Norma Cluster. We discuss the application of the model as a predictor of galaxy distances using only angular position and redshift measurements. By calibrating the model using measured distances to galaxies inside 3000 km/s, we show that, for a randomly-sampled 2MRS galaxy, improvement in the estimated distance over the application of Hubble's law is expected to be 30%, and considerably better in the proximity of clusters. We test the model using distance estimates from the SFI++ sample, and find evidence for improvement over the application of Hubble's law to galaxies inside 4000 km/s, although the performance varies depending on the location of the target. This work has been supported by NSF grant AST 0406906 and the Massachusetts Institute of Technology Bruno Rossi and Whiteman Fellowships.

MASSIVE STARS IN THE LOCAL GROUP: Implications for Stellar Evolution and Star Formation

NASA Astrophysics Data System (ADS)

Massey, Philip

The galaxies of the Local Group serve as important laboratories for understanding the physics of massive stars. Here I discuss what is involved in identifying various kinds of massive stars in nearby galaxies: the hydrogen-burning O-type stars and their evolved He-burning evolutionary descendants, the luminous blue variables, red supergiants, and Wolf-Rayet stars. Primarily I review what our knowledge of the massive star population in nearby galaxies has taught us about stellar evolution and star formation. I show that the current generation of stellar evolutionary models do well at matching some of the observed features and provide a look at the sort of new observational data that will provide a benchmark against which new models can be evaluated.

Where Are All of the Gas-bearing Local Dwarf Galaxies? Quantifying Possible Impacts of Reionization

NASA Astrophysics Data System (ADS)

Tollerud, Erik J.; Peek, J. E. G.

2018-04-01

We present an approach for comparing the detections and non-detections of Local Group (LG) dwarf galaxies in large H I surveys to the predictions of a suite of n-body simulations of the LG. This approach depends primarily on a set of empirical scaling relations to connect the simulations to the observations, rather than making strong theoretical assumptions. We then apply this methodology to the Galactic Arecibo L-band Feed Array Hi (GALFA-HI) Compact Cloud Catalog (CCC), and compare it to the suite Exploring the Local Volume In Simulations (ELVIS) of simulations. This approach reveals a strong tension between the naïve results of the model and the observations: while there are no LG dwarfs in the GALFA-HI CCC, the simulations predict ∼10. Applying a simple model of reionization can resolve this tension by preventing low-mass halos from forming gas. However, and if this effect operates as expected, the observations provide a constraint on the mass scale of the dwarf galaxy that reionization impacts. Combined with the observed properties of Leo T, the halo virial mass scale at which reionization impacts dwarf galaxy gas content is constrained to be ∼ {10}8.5 {M}ȯ , independent of any assumptions about star formation.

Galaxy Group Stephan's Quintet Video File HubbleMinute: Battle Royale in Stephan's Quintet

NASA Technical Reports Server (NTRS)

2001-01-01

The Hubble Space Telescope's closeup view of Stephan's Quintet, a group of five galaxies, reveals a string of brighter star clusters that separate like a diamond necklace. Astronomers studying the compact galaxy group Stephan's Quintet have seen creative destruction in the many collisions taking place among its galaxies. This HubbleMinute discusses what astronomers are learning and hope to learn from exploring the quintet.

Central Stellar Mass Deficits in the Bulges of Local Lenticular Galaxies, and the Connection with Compact z ~ 1.5 Galaxies

NASA Astrophysics Data System (ADS)

Dullo, Bililign T.; Graham, Alister W.

2013-05-01

We have used the full radial extent of images from the Hubble Space Telescope's Advanced Camera for Surveys and Wide Field Planetary Camera 2 to extract surface brightness profiles from a sample of six, local lenticular galaxy candidates. We have modeled these profiles using a core-Sérsic bulge plus an exponential disk model. Our fast rotating lenticular disk galaxies with bulge magnitudes MV <~ -21.30 mag have central stellar deficits, suggesting that these bulges may have formed from "dry" merger events involving supermassive black holes (BHs) while their surrounding disk was subsequently built up, perhaps via cold gas accretion scenarios. The central stellar mass deficits M def are roughly 0.5-2 M BH (BH mass), rather than ~10-20 M BH as claimed from some past studies, which is in accord with core-Sérsic model mass deficit measurements in elliptical galaxies. Furthermore, these bulges have Sérsic indices n ~3, half-light radii Re < 2 kpc and masses >1011 M ⊙, and therefore appear to be descendants of the compact galaxies reported at z ~ 1.5-2. Past studies which have searched for these local counterparts by using single-component galaxy models to provide the z ~ 0 size comparisons have overlooked these dense, compact, and massive bulges in today's early-type disk galaxies. This evolutionary scenario not only accounts for what are today generally old bulges—which must be present in z ~ 1.5 images—residing in what are generally young disks, but it eliminates the uncomfortable suggestion of a factor of three to five growth in size for the compact, z ~ 1.5 galaxies that are known to possess infant disks.

“Local” Dark Energy Outflows Around Galaxy Groups and Rich Clusters

NASA Astrophysics Data System (ADS)

Byrd, Gene G.; Chernin, A. D.; Teerikorpi, P.; Dolgachev, V. P.; Kanter, A. A.; Domozhilova, L. M.; Valtonen, M.

2013-01-01

First detected at large Gpc distances, dark energy is a vacuum energy formulated as Einstein's cosmological constant, Λ. We have found its effects on “small” 1-3 Mpc scales in our Local Group. We have now found these effects in other nearby groups using member Doppler shifts and 3D distances from group centers (Cen A-M83; M81-M82; CV I). For the larger 20-30 Mpc Virgo and Fornax clusters, we now have found similar effects. Observationally, for both groups and clusters, gravity dominates a bound central system. The system gravitation and dark energy create a “zero-gravity” radius (R_{ZG}) from the center where the two balance. Smaller members bound inside R_{ZG} may be pulled out along with the less bound members which recede farther. A linear increase of recession with distance results which approaches a linear global Hubble law. These outflows are seen around groups in cosmological simulations which include galaxies as small as ~10^{-4} of the group mass. Scaled plots of asymptotic recessional velocity, V/(H(R_{ZG})), versus distance/ R_{ZG} of the outer galaxies are very similar for both the small groups and large clusters. This similarity on 1-30 Mpc scales suggests that a quasi-stationary bound central component and an expanding outflow applies to a wide range of groups and clusters due to small scale action of dark energy. Our new text book: Byrd, G., Chernin, A., Terrikorpi, P. and Valtonen, M. 2012, "Paths to Dark Energy: Theory and Observation," de Gruyter, Berlin/Boston, contains background and cosmological simulation plots. Group data and scaled plots are in our new article: A. D. Chernin, P. Teerikorpi, V. P. Dolgachev, A. A. Kanter, L. M. Domozhilova, M. J. Valtonen, and G. G. Byrd, 2012, Astronomy Reports, Vol. 56 , p. 653-669.

Reproducing the local and global morphological segregation between S and S0 galaxies in rich clusters by simple ram-pressure stripping

NASA Astrophysics Data System (ADS)

Solanes, Jose M.; Salvador-Sole, Eduardo

1992-08-01

We calculate the morphological segregation in rich galaxy clusters expected to arise from the possible evolution of S galaxies into S0 galaxies via the gas removal of their disks by ram-pressure stripping. The calculation is run on Monte Carlo simulations by following individual S galaxies in the potential well of a spherical anisotropic cluster making use of Gunn and Gott's (1972) stripping condition. The results are compared with both Dressler's (1980) local type/density relation and a global population-richness correlation inferred from real data in the present work. We find that, contrary to a rather extended opinion, this evolution scheme reproduces very well the observed morphological segregation between S and S0 galaxies in rich clusters provided that the initial populations are close to those i dense loose groups.

The Galaxy Color-Magnitude Diagram in the Local Universe from GALEX and SDSS Data

NASA Astrophysics Data System (ADS)

Wyder, T. K.; GALEX Science Team

2005-12-01

We present the relative density of galaxies in the local universe as a function of their r-band absolute magnitudes and ultraviolet minus r-band colors. The Sloan Digital Sky Survey (SDSS) main galaxy sample selected in the r-band was matched with a sample of galaxies from the Galaxy Evolution Explorer (GALEX) Medium Imaging Survey in both the far-UV (FUV) and near-UV (NUV) bands. Simlar to previous optical studies, the distribution of galaxies in (FUV-r) and (NUV-r) is bimodal with well-defined blue and red sequences. We compare the distribution of galaxies in these colors with both the D4000 index measured from the SDSS spectra as well as the SDSS (u-r) color.

Imprints of local lightcone \\ projection effects on the galaxy bispectrum. Part II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jolicoeur, Sheean; Umeh, Obinna; Maartens, Roy

General relativistic imprints on the galaxy bispectrum arise from observational (or projection) effects. The lightcone projection effects include local contributions from Doppler and gravitational potential terms, as well as lensing and other integrated contributions. We recently presented for the first time, the correction to the galaxy bispectrum from all local lightcone projection effects up to second order in perturbations. Here we provide the details underlying this correction, together with further results and illustrations. For moderately squeezed shapes, the correction to the Newtonian prediction is ∼ 30% on equality scales at z ∼ 1. We generalise our recent results to includemore » the contribution, up to second order, of magnification bias (which affects some of the local terms) and evolution bias.« less

THE MERGER HISTORY, ACTIVE GALACTIC NUCLEUS, AND DWARF GALAXIES OF HICKSON COMPACT GROUP 59

DOE Office of Scientific and Technical Information (OSTI.GOV)

Konstantopoulos, I. S.; Charlton, J. C.; Brandt, W. N.

2012-01-20

Compact group galaxies often appear unaffected by their unusually dense environment. Closer examination can, however, reveal the subtle, cumulative effects of multiple galaxy interactions. Hickson Compact Group (HCG) 59 is an excellent example of this situation. We present a photometric study of this group in the optical (Hubble Space Telescope), infrared (Spitzer), and X-ray (Chandra) regimes aimed at characterizing the star formation and nuclear activity in its constituent galaxies and intra-group medium. We associate five dwarf galaxies with the group and update the velocity dispersion, leading to an increase in the dynamical mass of the group of up to amore » factor of 10 (to 2.8 Multiplication-Sign 10{sup 13} M{sub Sun }), and a subsequent revision of its evolutionary stage. Star formation is proceeding at a level consistent with the morphological types of the four main galaxies, of which two are star-forming and the other are two quiescent. Unlike in some other compact groups, star-forming complexes across HCG 59 closely follow mass-radius scaling relations typical of nearby galaxies. In contrast, the ancient globular cluster populations in galaxies HCG 59A and B show intriguing irregularities, and two extragalactic H II regions are found just west of B. We age-date a faint stellar stream in the intra-group medium at {approx}1 Gyr to examine recent interactions. We detect a likely low-luminosity active galactic nucleus in HCG 59A by its {approx}10{sup 40} erg s{sup -1} X-ray emission; the active nucleus rather than star formation can account for the UV+IR spectral energy distribution. We discuss the implications of our findings in the context of galaxy evolution in dense environments.« less

The Role of Star Formation in Radio-Loud Galaxy Groups

NASA Astrophysics Data System (ADS)

Herbst, Hanna; Wilcots, E.; Hess, K.

2010-01-01

X-ray observations have shown that additional non-gravitational processes are required to explain the heating of the intergalactic medium in galaxy groups. The two most likely processes are galactic outflows from starbursts and feedback from AGN. Here, we look at star formation as a possible additional heating mechanism in X-ray luminous groups such as NGC 741, NGC 1052, NGC 524, and NGC 1587. We report on the results of optical imaging of these groups carried out using the WIYN 3.5m telescope with a specific emphasis on measuring the star formation rates of the resident galaxies in each group and estimating the impact of that star formation on the thermodynamics of the intragroup medium.

Internal kinematics of disk galaxies in the local universe

NASA Astrophysics Data System (ADS)

Catinella, Barbara

2005-11-01

This dissertation makes use of a homogeneous sample of several thousand normal, non-interacting, spiral galaxies, for which I-band photometry and optical and/ or radio spectroscopy are available, to investigate the average kinematic properties of disk systems at low redshifts ( z [Special characters omitted.] 0.1). New long-slit Ha rotation curves (RCs) for 402 galaxies, which were incorporated into the larger sample, are presented in this work. The main goals of this thesis are: (a) The definition of a set of average, or template , RCs in bins covering a wide range of galaxy luminosity. The template relations represent an accurate description of the average circular velocity field of local spiral galaxies, and are intended to be a standard reference for more distant samples and to constrain theoretical models of galactic disks. (b) The characterization of the systematics associated with different velocity width measurement techniques, and the derivation of a robust measure of rotational velocity to be used for applications of the Tully-Fisher (TF) distance method. A direct cross-calibration of the optical and radio widths has been obtained. (c) The assessment of the impact of the limitations on optical line widths extracted from fixed apertures, such as those being collected for ~10 6 galaxies by the on-going Sloan Digital Sky Survey (SDSS). Since the SDSS fiber technique generally does not sample the full extent of a galaxy RC, the observed line widths yield rotational width measurements that depend on the redshifts of the objects, on the physical sizes of their line-emitting regions, and on the intrinsic shapes of their RCs. Numerical simulations of these biases have been carried out for galaxies with realistic circular velocity fields (described by the template RCs) in the redshift range covered by the SDSS spectroscopic sample. Statistical corrections to be applied to the aperture line widths as a function of galaxy redshift and luminosity have been derived

The Dragonfly Nearby Galaxies Survey. III. The Luminosity Function of the M101 Group

NASA Astrophysics Data System (ADS)

Danieli, Shany; van Dokkum, Pieter; Merritt, Allison; Abraham, Roberto; Zhang, Jielai; Karachentsev, I. D.; Makarova, L. N.

2017-03-01

We obtained follow-up HST observations of the seven low surface brightness galaxies discovered with the Dragonfly Telephoto Array in the field of the massive spiral galaxy M101. Out of the seven galaxies, only three were resolved into stars and are potentially associated with the M101 group at D = 7 Mpc. Based on HST ACS photometry in the broad F606W and F814W filters, we use a maximum likelihood algorithm to locate the Tip of the Red Giant Branch in galaxy color-magnitude diagrams. Distances are {6.38}-0.35+0.35,{6.87}-0.30+0.21 and {6.52}-0.27+0.25 {Mpc} and we confirm that they are members of the M101 group. Combining the three confirmed low-luminosity satellites with previous results for brighter group members, we find the M101 galaxy group to be a sparsely populated galaxy group consisting of seven group members, down to M V = -9.2 mag. We compare the M101 cumulative luminosity function to that of the Milky Way and M31. We find that they are remarkably similar; in fact, the cumulative luminosity function of the M101 group gets even flatter for fainter magnitudes, and we show that the M101 group might exhibit the two known small-scale flaws in the ΛCDM model, namely “the missing satellite” problem and the “too big to fail” problem. Kinematic measurements of M101's satellite galaxies are required to determine whether the “too big to fail” problem does in fact exist in the M101 group.

MOND simulation suggests an origin for some peculiarities in the Local Group

NASA Astrophysics Data System (ADS)

Bílek, M.; Thies, I.; Kroupa, P.; Famaey, B.

2018-06-01

Context. The Milky Way (MW) and Andromeda (M 31) galaxies possess rotating planes of satellites. The formation of these planes has not been explained satisfactorily so far. It has been suggested that the MW and M 31 satellites are ancient tidal dwarf galaxies; this might explain their configuration. This suggestion gained support by an analytic backward-calculation of the relative MW-M 31 orbit in the MOND modified dynamics paradigm. The result implied that the galaxies experienced a close flyby 7-11 Gyr ago. Aims: Here we explore the Local Group history in MOND in more detail using a simplified first-ever self-consistent simulation. We describe the features induced by the encounter in the simulation and identify possible real counterparts of these features. Methods: The initial conditions were set to eventually roughly reproduce the observed MW and M 31 masses, effective radii, separation, relative velocity, and disk inclinations. We used the publicly available adaptive-mesh-refinement code Phantom of RAMSES. Results: Matter was transferred from the MW to M 31 along a tidal tail in the simulation. The encounter induced the formation of several structures resembling the peculiarities of the Local Group. Most notably are that 1) a rotating planar structure formed around M 31 from the transferred material. It had a size similar to the observed satellite plane and was oriented edge-on to the simulated MW, just as the real plane. 2) The same structure also resembled the tidal features observed around M 31 by its size and morphology. 3) A warp in the MW developed with an amplitude and orientation similar to that observed. 4) A cloud of particles formed around the simulated MW, with the extent of the actual MW satellite system. The encounter did not end by merging in a Hubble time. The simulated stellar disks also thickened as a result of the encounter. Conclusions: The simulation demonstrated that MOND might explain many peculiarities of the Local Group; this needs to

EVIDENCE FOR ELEVATED X-RAY EMISSION IN LOCAL LYMAN BREAK GALAXY ANALOGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Basu-Zych, Antara R.; Lehmer, Bret D.; Hornschemeier, Ann E.

2013-09-10

Our knowledge of how X-ray emission scales with star formation at the earliest times in the universe relies on studies of very distant Lyman break galaxies (LBGs). In this paper, we study the relationship between the 2-10 keV X-ray luminosity (L{sub X}), assumed to originate from X-ray binaries (XRBs), and star formation rate (SFR) in ultraviolet (UV) selected z < 0.1 Lyman break analogs (LBAs). We present Chandra observations for four new Galaxy Evolution Explorer selected LBAs. Including previously studied LBAs, Haro 11 and VV 114, we find that LBAs demonstrate L{sub X}/SFR ratios that are elevated by {approx}1.5{sigma} comparedmore » to local galaxies, similar to the ratios found for stacked LBGs in the early universe (z > 2). Unlike some of the composite LBAs studied previously, we show that these LBAs are unlikely to harbor active galactic nuclei, based on their optical and X-ray spectra and the spatial distribution of the X-rays in three spatially extended cases. Instead, we expect that high-mass X-ray binaries (HMXBs) dominate the X-ray emission in these galaxies, based on their high specific SFRs (sSFRs {identical_to} SFR/M{sub *} {>=} 10{sup -9} yr{sup -1}), which suggest the prevalence of young stellar populations. Since both UV-selected populations (LBGs and LBAs) have lower dust attenuations and metallicities compared to similar samples of more typical local galaxies, we investigate the effects of dust extinction and metallicity on the L{sub X}/SFR for the broader population of galaxies with high sSFRs (>10{sup -10} yr{sup -1}). The estimated dust extinctions (corresponding to column densities of N{sub H} < 10{sup 22} cm{sup -2}) are expected to have insignificant effects on observed L{sub X}/SFR ratio for the majority of galaxy samples. We find that the observed relationship between L{sub X}/SFR and metallicity appears consistent with theoretical expectations from XRB population synthesis models. Therefore, we conclude that lower metallicities

Groups of two galaxies in SDSS: implications of colours on star formation quenching time-scales

NASA Astrophysics Data System (ADS)

Trinh, Christopher Q.; Barton, Elizabeth J.; Bullock, James S.; Cooper, Michael C.; Zentner, Andrew R.; Wechsler, Risa H.

2013-11-01

We have devised a method to select galaxies that are isolated in their dark matter halo (N = 1 systems) and galaxies that reside in a group of exactly two (N = 2 systems). Our N = 2 systems are widely separated (up to ˜200 h-1 kpc), where close galaxy-galaxy interactions are not dominant. We apply our selection criteria to two volume-limited samples of galaxies from Sloan Digital Sky Survey Data Release 6 (SDSS DR6) with Mr - 5 log10 h ≤ -19 and -20 to study the effects of the environment of very sparse groups on galaxy colour. For satellite galaxies in a group of two, we find a red excess attributed to star formation quenching of 0.15 ± 0.01 and 0.14 ± 0.01 for the -19 and -20 samples, respectively, relative to isolated galaxies of the same stellar mass. Assuming N = 1 systems are the progenitors of N = 2 systems, an immediate-rapid star formation quenching scenario is inconsistent with these observations. A delayed-then-rapid star formation quenching scenario with a delay time of 3.3 and 3.7 Gyr for the -19 and -20 samples, respectively, yields a red excess prediction in agreement with the observations. The observations also reveal that central galaxies in a group of two have a slight blue excess of 0.06 ± 0.02 and 0.02 ± 0.01 for the -19 and -20 samples, respectively, relative to N = 1 populations of the same stellar mass. Our results demonstrate that even the environment of very sparse groups of luminous galaxies influence galaxy evolution and in-depth studies of these simple systems are an essential step towards understanding galaxy evolution in general.

A blind HI search for galaxies in the northern Zone of Avoidance

NASA Astrophysics Data System (ADS)

Rivers, Andrew James

Searches for galaxies in the nearby and distant universe have long focused in the direction of the Galactic poles, or perpendicular to the plane of the Milky Way. Dust concentrated in the Milky Way's disk absorbs and scatters light and therefore precludes easy optical detection of extragalactic sources in this ``Zone of Avoidance'' (ZOA). The Dwingeloo Obscured Galaxies Survey (DOGS) was a 21-cm blind survey for galaxies hidden in the northern ZOA. Dust is transparent at radio wavelengths and therefore the survey is not biased against detection of galaxies near the Galactic plane. The DOGS project was designed to reveal hidden dynamically important nearby galaxies and to help ``fill in the blanks'' in the local large scale structure. During the survey and subsequent followup observations, 43 galaxies were detected; 28 of these were previously unknown. Obscuration by dust could effectively hide a massive member of the Local Group. This survey rules out the existence of a hidden gas-rich dynamically important source. The possibility of gas-poor elliptical galaxies and low-mass dwarfs remains; the low velocity of one detected dwarf irregular galaxy relative to the Milky Way indicates possible membership in the Local Group. Other nearby galaxies detected by DOGS were linked to the IC 342/Maffei group and to the nearby galaxy NGC 6946. Of the five galaxies in the IC 342/Maffei group, three were unknown at the time of the survey. Derived group properties indicate the group consists of two separate physical groups which appear close together in the sky. The five sources near NGC 6946 support the identification of a new nearby group associated with this large spiral galaxy. The distribution of massive spiral galaxies compared to low-mass dwarf galaxies may be used to test theories of structure formation. In a universe dominated by Cold Dark Matter (CDM) dwarf galaxies are more evenly distributed and are a more accurate tracer of the mass distribution. Open universe models

The frequency and properties of young tidal dwarf galaxies in nearby gas-rich groups

NASA Astrophysics Data System (ADS)

Lee-Waddell, K.; Spekkens, K.; Chandra, P.; Patra, N.; Cuillandre, J.-C.; Wang, J.; Haynes, M. P.; Cannon, J.; Stierwalt, S.; Sick, J.; Giovanelli, R.

2016-08-01

We present high-resolution Giant Metrewave Radio Telescope (GMRT) H I observations and deep Canada-France-Hawaii Telescope (CFHT) optical imaging of two galaxy groups: NGC 4725/47 and NGC 3166/9. These data are part of a multi-wavelength unbiased survey of the gas-rich dwarf galaxy populations in three nearby interacting galaxy groups. The NGC 4725/47 group hosts two tidal knots and one dwarf irregular galaxy (dIrr). Both tidal knots are located within a prominent H I tidal tail, appear to have sufficient mass (Mgas ≈ 108 M⊙) to evolve into long-lived tidal dwarf galaxies (TDGs) and are fairly young in age. The NGC 3166/9 group contains a TDG candidate, AGC 208457, at least three dIrrs and four H I knots. Deep CFHT imaging confirms that the optical component of AGC 208457 is bluer - with a 0.28 mag g - r colour - and a few Gyr younger than its purported parent galaxies. Combining the results for these groups with those from the NGC 871/6/7 group reported earlier, we find that the H I properties, estimated stellar ages and baryonic content of the gas-rich dwarfs clearly distinguish tidal features from their classical counterparts. We optimistically identify four potentially long-lived tidal objects associated with three separate pairs of interacting galaxies, implying that TDGs are not readily produced during interaction events as suggested by some recent simulations. The tidal objects examined in this survey also appear to have a wider variety of properties than TDGs of similar mass formed in current simulations of interacting galaxies, which could be the result of pre- or post-formation environmental influences.

Andromeda Galaxy

NASA Technical Reports Server (NTRS)

2003-01-01

[figure removed for brevity, see original site]

This image is a Galaxy Evolution Explorer observation of the large galaxy in Andromeda, Messier 31. The Andromeda galaxy is the most massive in the local group of galaxies that includes our Milky Way. Andromeda is the nearest large galaxy to our own. The image is a mosaic of 10 separate Galaxy Evolution Explorer images taken in September, 2003. The color image (with near ultraviolet shown by red and far ultraviolet shown by blue) shows blue regions of young, hot, high mass stars tracing out the spiral arms where star formation is occurring, and the central orange-white 'bulge' of old, cooler stars formed long ago. The star forming arms of Messier 31 are unusual in being quite circular rather than the usual spiral shape. Several companion galaxies can also be seen. These include Messier 32, a dwarf elliptical galaxy directly below the central bulge and just outside the spiral arms, and Messier 110 (M110), which is above and to the right of the center. M110 has an unusual far ultraviolet bright core in an otherwise 'red,' old star halo. Many other regions of star formation can be seen far outside the main body of the galaxy.

Local starburst galaxies and their descendants. Statistics from the Sloan Digital Sky Survey

NASA Technical Reports Server (NTRS)

Bergvall, Nils; Marquart, Thomas; Way, Michael J.; Blomqvist, Anna; Holst, Emma; Ostlin, Goran; Zackrisson, Erik

2016-01-01

Despite strong interest in the starburst phenomenon in extragalactic astronomy, the concept remains ill-defined. Here we use a strict definition of starburst to examine the statistical properties of starburst galaxies in the local universe. We also seek to establish links between starburst galaxies, post-starburst (hereafter postburst) galaxies, and active galaxies. Data were selected from the Sloan Digital Sky Survey DR7. We applied a novel method of treating dust attenuation and derive star formation rates, ages, and stellar masses assuming a two-component stellar population model. Dynamical masses are calculated from the width of the H-alpha line. These masses agree excellently with the photometric masses. The mass (gas+stars) range is approximately 10( exp 9) - 10(exp 11.5) solar mass. As a selection criterion for starburst galaxies, we use, the birthrate parameter, b = SFR/SFR, requiring that b is greater than 3. For postburst galaxies, we use, the equivalent width of Hdelta in absorption with the criterion EW (sub Hdelta_abs) is greater than 6 A. Results. We find that only 1% of star-forming galaxies are starburst galaxies. They contribute 3-6% to the stellar production and are therefore unimportant for the local star formation activity. The median starburst age is 70 Myr roughly independent of mass, indicating that star formation is mainly regulated by local feedback processes. The b-parameter strongly depends on burst age. Values close to b = 60 are found at ages approximately 10 Myr, while almost no starbursts are found at ages greater than 1 Gyr. The median baryonic burst mass fraction of sub-L galaxies is 5% and decreases slowly towards high masses. The median mass fraction of the recent burst in the postburst sample is 5-10%. A smaller fraction of the postburst galaxies, however, originates in non-bursting galaxies. The age-mass distribution of the postburst progenitors (with mass fractions is greater than 3%) is bimodal with a break at logM(solar mass

The Enigmatic Local Hubble Flow: Probing the Nearby Peculiar Velocity Field with Consistent Distances to Neighboring Galaxies.

NASA Astrophysics Data System (ADS)

Mendez, B.; Davis, M.; Newman, J.; Madore, B. F.; Freedman, W. L.; Moustakas, J.

2002-12-01

The properties of the velocity field in the local volume (cz < 550 km s-1) have been difficult to constrain due to a lack of a consistent set of galaxy distances. The sparse observations available to date suggest a remarkably quiet flow, with little deviation from a pure Hubble law. However, velocity field models based on the distribution of galaxies in the 1.2 Jy IRAS redshift survey, predict a quadrupolar flow pattern locally with strong infall at the poles of the local Supergalactic plane. In an attempt to resolve this discrepency, we probe the local velocity field and begin to establish a consistent set of galactic distances. We have obtained images of nearby galaxies in I, V, and B bands from the W.M. Keck Observatory and in F814W and F555W filters from the Hubble Space Telescope. Where these galaxies are well resolved into stars we can use the Tip of the Red Giant Branch (TRGB) as a distance indicator. Using a maximum likelihood analysis to quantitatively measure the I magnitude of the TRGB we determine precise distances to several nearby galaxies. We supplement that dataset with published distances to local galaxies measured using Cepheids, Surface Brightness Fluctuations, and the TRGB. With these data we find that the amplitude of the local flow is roughly half that expected in linear theory and N-body simulations; thus the enigma of cold local flows persists. This work was supported in part by NASA through a grant from the Space Telescope Science Institute and a Predoctoral Fellowship for Minorities from the Ford Foundation.

Metallicity inhomogeneities in local star-forming galaxies as a sign of recent metal-poor gas accretion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sánchez Almeida, J.; Morales-Luis, A. B.; Muñoz-Tuñón, C.

2014-03-01

We measure the oxygen metallicity of the ionized gas along the major axis of seven dwarf star-forming galaxies. Two of them, SDSSJ1647+21 and SDSSJ2238+14, show ≅0.5 dex metallicity decrements in inner regions with enhanced star formation activity. This behavior is similar to the metallicity drop observed in a number of local tadpole galaxies by Sánchez Almeida et al., and was interpreted as showing early stages of assembling in disk galaxies, with the star formation sustained by external metal-poor gas accretion. The agreement with tadpoles has several implications. (1) It proves that galaxies other than the local tadpoles present the samemore » unusual metallicity pattern. (2) Our metallicity inhomogeneities were inferred using the direct method, thus discarding systematic errors usually attributed to other methods. (3) Taken together with the tadpole data, our findings suggest a threshold around one-tenth the solar value for the metallicity drops to show up. Although galaxies with clear metallicity drops are rare, the physical mechanism responsible for them may sustain a significant part of the star formation activity in the local universe. We argue that the star formation dependence of the mass-metallicity relationship, as well as other general properties followed by most local disk galaxies, is naturally interpreted as side effects of pristine gas infall. Alternatives to the metal-poor gas accretion are examined as well.« less

Dark Galaxies and Lost Baryons (IAU S244)

NASA Astrophysics Data System (ADS)

Davies, Jonathan I.; Disney, Michael J.

2008-05-01

Preface; Conference prelims; The HI that barked in the night M. J. Disney; The detection of dark galaxies in blind HI surveys J. I. Davies; Red haloes of galaxies - reservoirs of baryonic dark matter? E. Zackrisson, N. Bergvall, C. Flynn, G. Ostlin, G. Micheva and B. Baldwell; Constraints on dark and visible mass in galaxies from strong gravitational lensing S. Dye and S. Warren; Lost baryons at low redshift S. Mathur, F. Nicastro and R. Williams; Observed properties of dark matter on small spatial scales R. Wyse and G. Gilmore; The mass distribution in spiral galaxies P. Salucci; Connecting lost baryons and dark galaxies via QSO absorption lines T. Tripp; ALFALFA: HI cosmology in the local universe R. Giovanelli; The ALFALFA search for (almost) dark galaxies across the HI mass function M. Haynes; HI clouds detected towards Virgo with the Arecibo Legacy Fast ALFA Survey B. Kent; Cosmic variance in the HI mass function S. Schneider; The Arecibo Galaxy Environments Survey - potential for finding dark galaxies and results so far R. Minchin et al.; Free-floating HI clouds in the M81 group E. Brinks, F. Walter and E. Skillman; Where are the stars in dark galaxies J. Rosenberg, J. Salzer and J. Cannon; The halo by halo missing baryon problem S. McGaugh; The local void is really empty R. Tully; Voids in the local volume: a limit on appearance of a galaxy in a dark matter halo A. Tikhonov and A. Klypin; Dim baryons in the cosmic web C. Impey; A census of baryons in galaxy clusters and groups A. Gonzalez, D. Zaritsky and A. Zabludo; Statistical properties of the intercluster light from SDSS image stacking S. Zibetti; QSO strong gravitational lensing and the detection of dark halos A. Maccio; Strong gravitational lensing: bright galaxies and lost dark-matter L. Koopmans; Mapping the distribution of luminous and dark matter in strong lensing galaxies I. Ferreras, P. Saha, L. Williams and S. Burles; Tidal debris posing as dark galaxies P. Duc, F. Bournaud and E. Brinks

KDG218, a nearby ultra-diffuse galaxy

NASA Astrophysics Data System (ADS)

Karachentsev, I. D.; Makarova, L. N.; Sharina, M. E.; Karachentseva, V. E.

2017-10-01

We present properties of the low-surface-brightness galaxy KDG218 observed with the HST/ACS. The galaxy has a half-light (effective) diameter of a e = 47″ and a central surface brightness of SB V (0) = 24.m4/□″. The galaxy remains unresolved with the HST/ACS, which implies its distance of D > 13.1 Mpc and linear effective diameter of A e > 3.0 kpc. We notice that KDG218 is most likely associated with a galaxy group around the massive lenticular NGC4958 galaxy at approximately 22 Mpc, or with the Virgo Southern Extension filament at approximately 16.5 Mpc. At these distances, the galaxy is classified as an ultra-diffuse galaxy (UDG) similar to those found in the Virgo, Fornax, and Coma clusters. We also present a sample of 15 UDG candidates in the Local Volume. These sample galaxies have the following mean parameters: 〈 D〉 = 5.1 Mpc, 〈 A e 〉 = 4.8 kpc, and 〈 SB B ( e)〉 = 27.m4/□″. All the local UDG candidates reside near massive galaxies located in the regions with the mean stellar mass density (within 1 Mpc) about 50 times greater than the average cosmic density. The local fraction of UDGs does not exceed 1.5% of the Local Volume population. We notice that the presented sample of local UDGs is a heterogeneous one containing irregular, transition, and tidal types, as well as objects consisting of an old stellar population.

Constraints on baryonic dark matter in the Galactic halo and Local Group

NASA Technical Reports Server (NTRS)

Richstone, Douglas; Gould, Andrew; Guhathakurta, Puragra; Flynn, Chris

1992-01-01

A four-color method and deep CCD data are used to search for very faint metal-poor stars in the direction of the south Galactic pole. The results make it possible to limit the contribution of ordinary old, metal-poor stars to the dynamical halo of the Galaxy or to the Local Group. The ratio of the mass of the halo to its ordinary starlight must be more than about 2000, unless the halo is very small. For the Local Group, this ratio is greater than about 400. If this local dark matter is baryonic, the process of compact-object formation must produce very few 'impurities' in the form of stars similar to those found in globular clusters. The expected number of unbound stars with MV not greater than 6 within 100 pc of the sun is less than 1 based on the present 90-percent upper limit to the Local Group starlight.

Neutral Hydrogen in the Local Group and around the Milky Way

NASA Astrophysics Data System (ADS)

Wolfe, Spencer A.

Galaxies in our universe must acquire fresh gas to continue forming new stars. A likely source of this material may be the gas that resides between galaxies. We do not, however, have a clear understanding of the specifics, such as its distribution. The first claimed detection of this "cosmic web" of material directly in emission was published a decade ago using the Westerbork Synthesis Radio Telescope in the Netherlands while surveying neutral hydrogen in the Local Group of galaxies. Later evidence, in the form of stellar surveys and test particle simulations, showed that a tidal origin of the gas was another possibility. More recent survey work of the Local Group, specifically between the galaxies M31 and M33, motivated us to map a section of the Westerbork emission using the Robert C . Byrd Green Bank Telescope (GBT). Our survey covers a 12 square degree area between M31 and M33, in which we reach 21 cm column density sensitivities of 1017.2 cm-2 after 400 hours of observations. These observations provide more than a factor of five better spatial resolution, and better than a factor of three in velocity resolution. Not only do we confirm the emission seen in the Westerbork data, we find that the hydrogen gas is composed of clouds a few kiloparsecs across, with properties suggesting they are a unique population to the Local Group. We conclude that the clouds are likely transient condensations from an intergalactic filament of gas, although a tidal feature cannot currently be ruled out. We also conducted GBT pointings to the northwest of M31 to search for the extended emission seen in the Westerbork data as well. What detections we find appear to be more related to the high velocity cloud population of M31. We are continuing to map other regions around M31 to search for more diffuse emission. We also present southern sky maps of the high velocity and intermediate velocity clouds around our own Milky Way, using 21 cm survey data from the Parkes telescope in

Some Like it Hot: Linking Diffuse X-Ray Luminosity, Baryonic Mass, and Star Formation Rate in Compact Groups of Galaxies

NASA Technical Reports Server (NTRS)

Desjardins, Tyler D.; Gallagher, Sarah C.; Hornschemeier, Ann E.; Mulchaey, John S.; Walker, Lisa May; Brandt, Willian N.; Charlton, Jane C.; Johnson, Kelsey E.; Tzanavaris, Panayiotis

2014-01-01

We present an analysis of the diffuse X-ray emission in 19 compact groups (CGs) of galaxies observed with Chandra. The hottest, most X-ray luminous CGs agree well with the galaxy cluster X-ray scaling relations in L(x-T) and (L(x-sigma), even in CGs where the hot gas is associated with only the brightest galaxy. Using Spitzer photometry, we compute stellar masses and classify Hickson CGs 19, 22, 40, and 42, and RSCGs 32, 44, and 86 as fossil groups using a new definition for fossil systems that includes a broader range of masses. We find that CGs with total stellar and Hi masses are great than or equal to 10(sup (11.3) solar mass are often X-ray luminous, while lower-mass CGs only sometimes exhibit faint, localized X-ray emission. Additionally, we compare the diffuse X-ray luminosity against both the total UV and 24 micron star formation rates of each CG and optical colors of the most massive galaxy in each of the CGs. The most X-ray luminous CGs have the lowest star formation rates, likely because there is no cold gas available for star formation, either because the majority of the baryons in these CGs are in stars or the X-ray halo, or due togas stripping from the galaxies in CGs with hot halos. Finally, the optical colors that trace recent star formation histories of the most massive group galaxies do not correlate with the X-ray luminosities of the CGs, indicating that perhaps the current state of the X-ray halos is independent of the recent history of stellar mass assembly in the most massive galaxies.

Tidal Disruption Event Host Galaxies in the Context of the Local Galaxy Population

NASA Astrophysics Data System (ADS)

Law-Smith, Jamie; Ramirez-Ruiz, Enrico; Ellison, Sara L.; Foley, Ryan J.

2017-11-01

We study the properties of tidal disruption event (TDE) host galaxies in the context of a catalog of ˜500,000 galaxies from the Sloan Digital Sky Survey. We explore whether selection effects can account for the overrepresentation of TDEs in E+A/post-starburst galaxies by creating matched galaxy samples. Accounting for possible selection effects due to black hole (BH) mass, redshift completeness, strong active galactic nucleus presence, bulge colors, and surface brightness can reduce the apparent overrepresentation of TDEs in E+A host galaxies by a factor of ˜4 (from ˜×100-190 to ˜×25-48), but cannot fully explain the preference. We find that TDE host galaxies have atypical photometric properties compared to similar, “typical” galaxies. In particular, TDE host galaxies tend to live in or near the “green valley” between star-forming and passive galaxies, and have bluer bulge colors ({{Δ }}(g-r)≈ 0.3 mag), lower half-light surface brightnesses (by ˜1 mag/arcsec2), higher Sérsic indices ({{Δ }}{n}{{g}}≈ 3), and higher bulge-to-total-light ratios ({{Δ }}B/T≈ 0.5) than galaxies with matched BH masses. We find that TDE host galaxies appear more centrally concentrated and that all have high galaxy Sérsic indices and B/T fractions—on average in the top 10% of galaxies of the same BH mass—suggesting a higher nuclear stellar density. We identify a region in the Sérsic index and BH mass parameter space that contains ˜2% of our reference catalog galaxies but ≥slant 60 % of TDE host galaxies. The unique photometric properties of TDE host galaxies may be useful for selecting candidate TDEs for spectroscopic follow-up observations in large transient surveys.

Census of the Local Universe (CLU): Classification of Galaxy Candidates in Narrowband Images Using Machine Learning

NASA Astrophysics Data System (ADS)

Zhang, Chaoran; Van Sistine, Anglea; Kaplan, David; Brady, Patrick; Cook, David O.; Kasliwal, Mansi

2018-01-01

A complete catalog of galaxies in the local universe is critical for efficient electromagnetic follow-up of gravitational wave events (EMGW). The Census of the Local Universe (CLU; Cook et al. 2017, in preparation) aims to provide a galaxy catalog out to 200 Mpc that is as complete as possible. CLU has recently completed an Hα survey of ~3π of the sky with the goal of cataloging those galaxies that are likely hosts of EMGW events. Here, we present a tool we developed using machine learning technology to classify sources extracted from the Hα narrowband images within 200Mpc. In this analysis we find we are able to recover more galaxies compared to selections based on Hα colors alone.

The Little Cub: Discovery of an Extremely Metal-poor Star-forming Galaxy in the Local Universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsyu, Tiffany; Prochaska, J. Xavier; Bolte, Michael

We report the discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local universe, found in the constellation Ursa Major (a.k.a. the Great Bear). We first identified the Little Cub as a candidate metal-poor galaxy based on its Sloan Digital Sky Survey photometric colors, combined with spectroscopy using the Kast spectrograph on the Shane 3 m telescope at Lick Observatory. In this Letter, we present high-quality spectroscopic data taken with the Low Resolution Imaging Spectrometer at Keck Observatory, which confirm the extremely metal-poor nature of this galaxy. Based on the weak [O iii] λ 4363 Å emissionmore » line, we estimate a direct oxygen abundance of 12 + log(O/H) = 7.13 ± 0.08, making the Little Cub one of the lowest-metallicity star-forming galaxies currently known in the local universe. The Little Cub appears to be a companion of the spiral galaxy NGC 3359 and shows evidence of gas stripping. We may therefore be witnessing the quenching of a near-pristine galaxy as it makes its first passage about a Milky Way–like galaxy.« less

The Little Cub: Discovery of an Extremely Metal-poor Star-forming Galaxy in the Local Universe

NASA Astrophysics Data System (ADS)

Hsyu, Tiffany; Cooke, Ryan J.; Prochaska, J. Xavier; Bolte, Michael

2017-08-01

We report the discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local universe, found in the constellation Ursa Major (a.k.a. the Great Bear). We first identified the Little Cub as a candidate metal-poor galaxy based on its Sloan Digital Sky Survey photometric colors, combined with spectroscopy using the Kast spectrograph on the Shane 3 m telescope at Lick Observatory. In this Letter, we present high-quality spectroscopic data taken with the Low Resolution Imaging Spectrometer at Keck Observatory, which confirm the extremely metal-poor nature of this galaxy. Based on the weak [O III] λ4363 Å emission line, we estimate a direct oxygen abundance of 12 + log(O/H) = 7.13 ± 0.08, making the Little Cub one of the lowest-metallicity star-forming galaxies currently known in the local universe. The Little Cub appears to be a companion of the spiral galaxy NGC 3359 and shows evidence of gas stripping. We may therefore be witnessing the quenching of a near-pristine galaxy as it makes its first passage about a Milky Way-like galaxy.

Dwarfs and Giants in the local flows of galaxies.

NASA Astrophysics Data System (ADS)

Chernin, A. D.; Emelyanov, N. V.; Karachentsev, I. D.

We use recent Hubble Space Telescope data on nearby dwarf and giant galaxies to study the dynamical structure and evolutionary trends of the local expansion flows of galaxies. It is found that antigravity of dark energy dominates the force field of the flows and makes them expand with acceleration. It also cools the flows and introduces to them the nearly linear velocity-distance relation with the time-rate close to the global Hubble's factor. There are grounds to expect that this is the universal physical regularity that is common not only for the nearby flows we studied here, but also for all the expansion flows of various spatial scales from the 1 Mpc scale and up to the scale of the global cosmological expansion.

Dwarf Galaxies and the Cosmic Web

NASA Astrophysics Data System (ADS)

Benítez-Llambay, Alejandro; Navarro, Julio F.; Abadi, Mario G.; Gottlöber, Stefan; Yepes, Gustavo; Hoffman, Yehuda; Steinmetz, Matthias

2013-02-01

We use a cosmological simulation of the formation of the Local Group of Galaxies to identify a mechanism that enables the removal of baryons from low-mass halos without appealing to feedback or reionization. As the Local Group forms, matter bound to it develops a network of filaments and pancakes. This moving web of gas and dark matter drifts and sweeps a large volume, overtaking many halos in the process. The dark matter content of these halos is unaffected but their gas can be efficiently removed by ram pressure. The loss of gas is especially pronounced in low-mass halos due to their lower binding energy and has a dramatic effect on the star formation history of affected systems. This "cosmic web stripping" may help to explain the scarcity of dwarf galaxies compared with the numerous low-mass halos expected in ΛCDM and the large diversity of star formation histories and morphologies characteristic of faint galaxies. Although our results are based on a single high-resolution simulation, it is likely that the hydrodynamical interaction of dwarf galaxies with the cosmic web is a crucial ingredient so far missing from galaxy formation models.

DWARF GALAXIES AND THE COSMIC WEB

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benitez-Llambay, Alejandro; Abadi, Mario G.; Navarro, Julio F.

2013-02-01

We use a cosmological simulation of the formation of the Local Group of Galaxies to identify a mechanism that enables the removal of baryons from low-mass halos without appealing to feedback or reionization. As the Local Group forms, matter bound to it develops a network of filaments and pancakes. This moving web of gas and dark matter drifts and sweeps a large volume, overtaking many halos in the process. The dark matter content of these halos is unaffected but their gas can be efficiently removed by ram pressure. The loss of gas is especially pronounced in low-mass halos due tomore » their lower binding energy and has a dramatic effect on the star formation history of affected systems. This 'cosmic web stripping' may help to explain the scarcity of dwarf galaxies compared with the numerous low-mass halos expected in {Lambda}CDM and the large diversity of star formation histories and morphologies characteristic of faint galaxies. Although our results are based on a single high-resolution simulation, it is likely that the hydrodynamical interaction of dwarf galaxies with the cosmic web is a crucial ingredient so far missing from galaxy formation models.« less

The Future of Stellar Populations Studies in the Milky Way and the Local Group

NASA Astrophysics Data System (ADS)

Majewski, Steven R.

2010-04-01

The last decade has seen enormous progress in understanding the structure of the Milky Way and neighboring galaxies via the production of large-scale digital surveys of the sky like 2MASS and SDSS, as well as specialized, counterpart imaging surveys of other Local Group systems. Apart from providing snaphots of galaxy structure, these “cartographic” surveys lend insights into the formation and evolution of galaxies when supplemented with additional data (e.g., spectroscopy, astrometry) and when referenced to theoretical models and simulations of galaxy evolution. These increasingly sophisticated simulations are making ever more specific predictions about the detailed chemistry and dynamics of stellar populations in galaxies. To fully exploit, test and constrain these theoretical ventures demands similar commitments of observational effort as has been plied into the previous imaging surveys to fill out other dimensions of parameter space with statistically significant intensity. Fortunately the future of large-scale stellar population studies is bright with a number of grand projects on the horizon that collectively will contribute a breathtaking volume of information on individual stars in Local Group galaxies. These projects include: (1) additional imaging surveys, such as Pan-STARRS, SkyMapper and LSST, which, apart from providing deep, multicolor imaging, yield time series data useful for revealing variable stars (including critical standard candles, like RR Lyrae variables) and creating large-scale, deep proper motion catalogs; (2) higher accuracy, space-based astrometric missions, such as Gaia and SIM-Lite, which stand to provide critical, high precision dynamical data on stars in the Milky Way and its satellites; and (3) large-scale spectroscopic surveys provided by RAVE, APOGEE, HERMES, LAMOST, and the Gaia spectrometer, which will yield not only enormous numbers of stellar radial velocities, but extremely comprehensive views of the chemistry of stellar

TESTING FOR A LARGE LOCAL VOID BY INVESTIGATING THE NEAR-INFRARED GALAXY LUMINOSITY FUNCTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keenan, R. C.; Wang, W.-H.; Barger, A. J.

2012-08-01

Recent cosmological modeling efforts have shown that a local underdensity on scales of a few hundred Mpc (out to z {approx} 0.1) could produce the apparent acceleration of the expansion of the universe observed via Type Ia supernovae. Several studies of galaxy counts in the near-infrared (NIR) have found that the local universe appears underdense by {approx}25%-50% compared with regions a few hundred Mpc distant. Galaxy counts at low redshifts sample primarily L {approx} L* galaxies. Thus, if the local universe is underdense, then the normalization of the NIR galaxy luminosity function (LF) at z > 0.1 should be highermore » than that measured for z < 0.1. Here we present a highly complete (>90%) spectroscopic sample of 1436 galaxies selected in the H band (1.6 {mu}m) to study the normalization of the NIR LF at 0.1 < z < 0.3 and address the question of whether or not we reside in a large local underdensity. Our survey sample consists of all galaxies brighter than 18th magnitude in the H band drawn from six widely separated fields at high Galactic latitudes, which cover a total of {approx}2 deg{sup 2} on the sky. We find that for the combination of our six fields, the product {phi}*L* at 0.1 < z < 0.3 is {approx}30% higher than that measured at lower redshifts. While our statistical errors in this measurement are on the {approx}10% level, we find the systematics due to cosmic variance may be larger still. We investigate the effects of cosmic variance on our measurement using the COSMOS cone mock catalogs from the Millennium Simulation and recent empirical estimates of cosmic variance. We find that our survey is subject to systematic uncertainties due to cosmic variance at the 15% level (1{sigma}), representing an improvement by a factor of {approx}2 over previous studies in this redshift range. We conclude that observations cannot yet rule out the possibility that the local universe is underdense at z < 0.1. The fields studied in this work have a large amount of

The disk averaged star formation relation for Local Volume dwarf galaxies

NASA Astrophysics Data System (ADS)

López-Sánchez, Á. R.; Lagos, C. D. P.; Young, T.; Jerjen, H.

2018-05-01

Spatially resolved H I studies of dwarf galaxies have provided a wealth of precision data. However these high-quality, resolved observations are only possible for handful of dwarf galaxies in the Local Volume. Future H I surveys are unlikely to improve the current situation. We therefore explore a method for estimating the surface density of the atomic gas from global H I parameters, which are conversely widely available. We perform empirical tests using galaxies with resolved H I maps, and find that our approximation produces values for the surface density of atomic hydrogen within typically 0.5 dex of the true value. We apply this method to a sample of 147 galaxies drawn from modern near-infrared stellar photometric surveys. With this sample we confirm a strict correlation between the atomic gas surface density and the star formation rate surface density, that is vertically offset from the Kennicutt-Schmidt relation by a factor of 10 - 30, and significantly steeper than the classical N = 1.4 of Kennicutt (1998). We further infer the molecular fraction in the sample of low surface brightness, predominantly dwarf galaxies by assuming that the star formation relationship with molecular gas observed for spiral galaxies also holds in these galaxies, finding a molecular-to-atomic gas mass fraction within the range of 5-15%. Comparison of the data to available models shows that a model in which the thermal pressure balances the vertical gravitational field captures better the shape of the ΣSFR-Σgas relationship. However, such models fail to reproduce the data completely, suggesting that thermal pressure plays an important role in the disks of dwarf galaxies.

Galaxy clusters in local Universe simulations without density constraints: a long uphill struggle

NASA Astrophysics Data System (ADS)

Sorce, Jenny G.

2018-06-01

Galaxy clusters are excellent cosmological probes provided that their formation and evolution within the large scale environment are precisely understood. Therefore studies with simulated galaxy clusters have flourished. However detailed comparisons between simulated and observed clusters and their population - the galaxies - are complicated by the diversity of clusters and their surrounding environment. An original way initiated by Bertschinger as early as 1987, to legitimize the one-to-one comparison exercise down to the details, is to produce simulations constrained to resemble the cluster under study within its large scale environment. Subsequently several methods have emerged to produce simulations that look like the local Universe. This paper highlights one of these methods and its essential steps to get simulations that not only resemble the local Large Scale Structure but also that host the local clusters. It includes a new modeling of the radial peculiar velocity uncertainties to remove the observed correlation between the decreases of the simulated cluster masses and of the amount of data used as constraints with the distance from us. This method has the particularity to use solely radial peculiar velocities as constraints: no additional density constraints are required to get local cluster simulacra. The new resulting simulations host dark matter halos that match the most prominent local clusters such as Coma. Zoom-in simulations of the latter and of a volume larger than the 30h-1 Mpc radius inner sphere become now possible to study local clusters and their effects. Mapping the local Sunyaev-Zel'dovich and Sachs-Wolfe effects can follow.

The frequency of very young galaxies in the local Universe: I. A test for galaxy formation and cosmological models

NASA Astrophysics Data System (ADS)

Tweed, D. P.; Mamon, G. A.; Thuan, T. X.; Cattaneo, A.; Dekel, A.; Menci, N.; Calura, F.; Silk, J.

2018-06-01

In the local Universe, the existence of very young galaxies (VYGs), having formed at least half their stellar mass in the last 1 Gyr, is debated. We predict the present-day fraction of VYGs among central galaxies as a function of galaxy stellar mass. For this, we apply to high mass resolution Monte Carlo halo merger trees (MCHMTs) three (one) analytical models of galaxy formation, where the ratio of stellar to halo mass (mass growth rate) is a function of halo mass and redshift. Galaxy merging is delayed until orbital decay by dynamical friction. With starbursts associated with halo mergers, our models predict typically 1 per cent of VYGs up to galaxy masses of m = 1010 M⊙, falling rapidly at higher masses, and VYGs are usually associated with recent major mergers of their haloes. Without these starbursts, two of the models have VYG fractions reduced by 1 or 2 dex at low or intermediate stellar masses, and VYGs are rarely associated with major halo mergers. In comparison, the state-of-the-art semi-analytical model (SAM) of Henriques et al. produces only 0.01 per cent of VYGs at intermediate masses. Finally, the Menci et al. SAM run on MCHMTs with Warm Dark Matter cosmology generates 10 times more VYGs at m < 108 M⊙ than when run with Cold Dark Matter. The wide range in these VYG fractions illustrates the usefulness of VYGs to constrain both galaxy formation and cosmological models.

Galaxy triplets in Sloan Digital Sky Survey Data Release 7 - II. A connection with compact groups?

NASA Astrophysics Data System (ADS)

Duplancic, Fernanda; O'Mill, Ana Laura; Lambas, Diego G.; Sodré, Laerte; Alonso, Sol

2013-08-01

We analyse a sample of 71 triplets of luminous galaxies derived from the work of O'Mill et al. We compare the properties of triplets and their members with those of control samples of compact groups, the 10 brightest members of rich clusters and galaxies in pairs. The triplets are restricted to have members with spectroscopic redshifts in the range 0.01 ≤ z ≤ 0.14 and absolute r-band luminosities brighter than Mr = -20.5. For these member galaxies, we analyse the stellar mass content, the star formation rates, the Dn(4000) parameter and (Mg - Mr) colour index. Since galaxies in triplets may finally merge in a single system, we analyse different global properties of these systems. We calculate the probability that the properties of galaxies in triplets are strongly correlated. We also study total star formation activity and global colours, and define the triplet compactness as a measure of the percentage of the system total area that is filled by the light of member galaxies. We concentrate in the comparison of our results with those of compact groups to assess how the triplets are a natural extension of these compact systems. Our analysis suggests that triplet galaxy members behave similarly to compact group members and galaxies in rich clusters. We also find that systems comprising three blue, star-forming, young stellar population galaxies (blue triplets) are most probably real systems and not a chance configuration of interloping galaxies. The same holds for triplets composed of three red, non-star-forming galaxies, showing the correlation of galaxy properties in these systems. From the analysis of the triplet as a whole, we conclude that, at a given total stellar mass content, triplets show a total star formation activity and global colours similar to compact groups. However, blue triplets show a high total star formation activity with a lower stellar mass content. From an analysis of the compactness parameter of the systems we find that light is even more

Do Perturbations from Dwarf Galaxies Produce Moving Groups in the Milky Way Disk?

NASA Astrophysics Data System (ADS)

Craig, Peter; Newberg, Heidi Jo; Chakrabarti, Sukanya

2018-01-01

We compare Solar neighborhood disk moving groups with velocity perturbations produced in hydrodynamic simulations of dwarf galaxy interactions with the disk. The hydrodynamic simulations were generated using Gadget 2, and mimic the interaction of the Sagittarius dwarf galaxy and several others with the Milky Way. The properties of the identified moving groups change as the simulations evolve. We identified moving groups in regions of the simulation that are within 1 kpc of the nominal location of the Sun (8 kpc from the Galactic center) that are similar to moving groups observed within the Milky Way. Such groups are found at locations all the way around the disk. This suggests that some of the groups that are observed near our sun are a result of an interaction between the Milky Way and a colliding dwarf galaxy. It also suggests that the existence of such groups here implies the existence of similar groups in other parts of the Milky Way.

BRIGHTEST SATELLITE GALAXY ALIGNMENT OF SLOAN DIGITAL SKY SURVEY GALAXY GROUPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Zhigang; Wang Yougang; Chen Xuelei

2013-05-01

We study the alignment signal between the distribution of the brightest satellite galaxies (BSGs) and the major axes of their host groups using the Sloan Digital Sky Survey group catalog constructed by Yang et al. After correcting for the effect of group ellipticity, a statistically significant ({approx}5{sigma}) major-axis alignment is detected and the alignment angle is found to be 43. Degree-Sign 0 {+-} 0. Degree-Sign 4. More massive and richer groups show a stronger BSG alignment. The BSG alignment around blue brightest central galaxies (BCGs) is slightly stronger than that around red BCGs. Red BSGs have a much stronger major-axismore » alignment than blue BSGs. Unlike BSGs, other satellites do not show very significant alignment with their group's major axis. We further explore BSG alignment using the semi-analytic model (SAM) constructed by Guo et al. In general, we found good agreement of the model with observations: BSGs in the SAM show a strong major-axis alignment that depends on group mass and richness in the same way as in observations and none of the other satellites exhibit prominent alignment. However, a discrepancy also exists in that the SAM shows a BSG color dependence opposite of that in observations, which is most probably induced by a missing large-scale environment ingredient in the SAM. The combination of two popular scenarios can explain the BSG alignment we detected. First, satellites merged into the group along the surrounding filaments, which are strongly aligned with the major axis of the group. Second, BSGs entered their host group more recently than other satellites, so they have preserved more information about their assembling history and major-axis alignment. In the SAM, we found positive evidence for the second scenario in the fact that BSGs merged into groups statistically more recently than other satellites. We also found that most of the BSGs (80%) were BCGs before they merged into groups and earlier merging BSGs tend to be

The Metallicity Evolution of Blue Compact Dwarf Galaxies from the Intermediate Redshift to the Local Universe

NASA Astrophysics Data System (ADS)

Lian, Jianhui; Hu, Ning; Fang, Guanwen; Ye, Chengyun; Kong, Xu

2016-03-01

We present oxygen abundance measurements for 74 blue compact dwarf (BCD) galaxies in the redshift range of [0.2, 0.5] using the strong-line method. The spectra of these objects are taken using Hectospec on the Multiple Mirror Telescope. More than half of these BCDs had dust attenuation corrected using the Balmer decrement method. For comparison, we also selected a sample of 2023 local BCDs from the Sloan Digital Sky Survey (SDSS) database. Based on the local and intermediate-z BCD samples, we investigated the cosmic evolution of the metallicity, star formation rate (SFR), and Dn(4000) index. Compared with local BCDs, the intermediate-z BCDs had a systematically higher R23 ratio but a similar O32 ratio. Interestingly, no significant deviation in the mass-metallicity (MZ) relation was found between the intermediate-z and local BCDs. Besides the metallicity, the intermediate-z BCDs also exhibited an SFR distribution that was consistent with local BCDs, suggesting a weak dependence on redshift. The intermediate-z BCDs seemed to be younger than the local BCDs with lower Dn(4000) index values. The insignificant deviation in the mass-metallicity and mass-SFR relations between intermediate-z and local BCDs indicates that the relations between the global parameters of low-mass compact galaxies may be universal. These results from low-mass compact galaxies could be used to place important observational constraints on galaxy formation and evolution models.

Exploring Satellite Galaxy Rotation Curves in the SAGA Survey

NASA Astrophysics Data System (ADS)

Rowland, Danielle; Tollerud, Erik; Watkins, Laura L.

2018-01-01

The Milky Way and its neighbors, known as the Local Group, have been extensively studied; however, it isn’t known if they are representative of similar galaxy groups in the larger universe. The SAGA Survey seeks to find and characterize satellite galaxies around 100 host galaxies that are analogous to the Milky Way to achieve a statistically-significant sample size for comparison to the Local Group. Candidate satellites were first identified using photometry, and then confirmed using redshifts determined from fiber spectroscopy; so far this has yielded 29 satellites around 8 host galaxies. This poster will detail the process of reducing further follow-up data on these 29 confirmed satellites that used the long-slit double spectrograph at Palomar Observatory. I will describe in detail the steps of bias/flat calibration, finding a dispersion solution, subtracting sky emissions, and combining red and blue side spectra to extract a complete 1D spectrum. I will also discuss how this follow-up data uniquely allows for determination of galaxy rotation curves that will help characterize the dark matter content for each satellite.

THE DISCOVERY OF SEVEN EXTREMELY LOW SURFACE BRIGHTNESS GALAXIES IN THE FIELD OF THE NEARBY SPIRAL GALAXY M101

DOE Office of Scientific and Technical Information (OSTI.GOV)

Merritt, Allison; Van Dokkum, Pieter; Abraham, Roberto, E-mail: allison.merritt@yale.edu

2014-06-01

Dwarf satellite galaxies are a key probe of dark matter and of galaxy formation on small scales and of the dark matter halo masses of their central galaxies. They have very low surface brightness, which makes it difficult to identify and study them outside of the Local Group. We used a low surface brightness-optimized telescope, the Dragonfly Telephoto Array, to search for dwarf galaxies in the field of the massive spiral galaxy M101. We identify seven large, low surface brightness objects in this field, with effective radii of 10-30 arcseconds and central surface brightnesses of μ {sub g} ∼ 25.5-27.5 magmore » arcsec{sup –2}. Given their large apparent sizes and low surface brightnesses, these objects would likely be missed by standard galaxy searches in deep fields. Assuming the galaxies are dwarf satellites of M101, their absolute magnitudes are in the range –11.6 ≲ M{sub V} ≲ –9.3 and their effective radii are 350 pc-1.3 kpc. Their radial surface brightness profiles are well fit by Sersic profiles with a very low Sersic index (n ∼ 0.3-0.7). The properties of the sample are similar to those of well-studied dwarf galaxies in the Local Group, such as Sextans I and Phoenix. Distance measurements are required to determine whether these galaxies are in fact associated with M101 or are in its foreground or background.« less

Mapping the Similarities of Spectra: Global and Locally-biased Approaches to SDSS Galaxies

NASA Astrophysics Data System (ADS)

Lawlor, David; Budavári, Tamás; Mahoney, Michael W.

2016-12-01

We present a novel approach to studying the diversity of galaxies. It is based on a novel spectral graph technique, that of locally-biased semi-supervised eigenvectors. Our method introduces new coordinates that summarize an entire spectrum, similar to but going well beyond the widely used Principal Component Analysis (PCA). Unlike PCA, however, this technique does not assume that the Euclidean distance between galaxy spectra is a good global measure of similarity. Instead, we relax that condition to only the most similar spectra, and we show that doing so yields more reliable results for many astronomical questions of interest. The global variant of our approach can identify very finely numerous astronomical phenomena of interest. The locally-biased variants of our basic approach enable us to explore subtle trends around a set of chosen objects. The power of the method is demonstrated in the Sloan Digital Sky Survey Main Galaxy Sample, by illustrating that the derived spectral coordinates carry an unprecedented amount of information.

VLA neutral hydrogen imaging of compact groups of galaxies. II - HCG 31, 44, and 79

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, B.A.; Mcmahon, P.M.; Van gorkom, J.H.

1991-06-01

Neutral hydrogen images of three compact groups of galaxies are presented: HCG 31, 44, and 79. The images were obtained with the very large array (VLA), an on-line Hanning smoothing was applied to the data, and the H I spectral channel was isolated. The images were made on the Pipeline, and were produced by means of a method described by Gorkon and Ekers (1988). The images of HCG 44 are compared with earlier Arecibo observations. The H I emission in HCG 44 is discovered within the galaxies, whereas the emission in 31 and 79 can be found throughout the groupmore » in clouds that are larger than the galaxies. Evidence of a relationship between the compact groups is found in the H I data, and the groups are considered to be merging into a single object. Some of the groups are theorized to be young amorphous galaxies where the H I is still bound to individual galaxies, and which have just begun to condense from the intergalactic medium. The kinematics of the gas are shown to vary, and a common gaseous envelope contains the dwarf galaxies. 42 refs.« less

A Census of Baryons in Galaxy Clusters and Groups

NASA Astrophysics Data System (ADS)

Gonzalez, Anthony H.; Zaritsky, Dennis; Zabludoff, Ann I.

2007-09-01

We determine the contribution of stars in galaxies, intracluster stars, and the intracluster medium to the total baryon budget in nearby galaxy clusters and groups. We find that the baryon mass fraction (fb≡Ωb/Ωm) within r500 is constant for systems with M500 between 6×1013 and 1×1015 Msolar. Although fb is lower than the WMAP value, the shortfall is on the order of both the observational systematic uncertainties and the depletion of baryons within r500 that is predicted by simulations. The data therefore provide no compelling evidence for undetected baryonic components, particularly any that would be expected to vary in importance with cluster mass. A unique feature of the current analysis is direct inclusion of the contribution of intracluster light (ICL) in the baryon budget. With the addition of the ICL to the stellar mass in galaxies, the increase in X-ray gas mass fraction with increasing total mass is entirely accounted for by a decrease in the total stellar mass fraction, supporting the argument that the behavior of both the stellar and X-ray gas components is dominated by a decrease in star formation efficiency in more massive environments. Within just the stellar component, the fraction of the total stellar luminosity in the central, giant brightest cluster galaxy (BCG) and ICL (hereafter the BCG+ICL component) decreases as velocity dispersion (σ) increases for systems with 145 km s-1<=σ<=1026 km s-1, suggesting that the BCG+ICL component, and in particular the dominant ICL component, grows less efficiently in higher mass environments. The degree to which this behavior arises from our sample selection, which favored systems with central, giant elliptical galaxies, remains unclear. A more robust result is the identification of low-mass groups with large BCG+ICL components, demonstrating that the creation of ``intracluster'' stars does not require a massive cluster environment. Within r500 and r200, the BCG+ICL contributes on average 40% and 33% of

The evolution of massive stars: bridging the gap in the Local Group

NASA Astrophysics Data System (ADS)

Massey, Philip; Neugent, Kathryn F.; Levesque, Emily M.

2017-09-01

The nearby galaxies of the Local Group can act as our laboratories in helping to bridge the gap between theory and observations. In this review, we will describe the complications of identifying samples of OB stars, yellow and red supergiants, and Wolf-Rayet stars, and what we have so far learned from these studies. This article is part of the themed issue 'Bridging the gap: from massive stars to supernovae'.

H I debris in the IC 1459 galaxy group

NASA Astrophysics Data System (ADS)

Saponara, Juliana; Koribalski, Bärbel S.; Benaglia, Paula; Fernández López, Manuel

2018-01-01

We present H I synthesis imaging of the giant elliptical galaxy IC 1459 and its surroundings with the Australia Telescope Compact Array. Our search for extended H I emission revealed a large complex of H I clouds near IC 1459, likely to be the debris from tidal interactions with neighbouring galaxies. The total H I mass (∼109 M⊙) in the detected clouds spans 250 kpc from the north-east of the gas-rich spiral NGC 7418A to the south-east of IC 1459. The extent and mass of the H I debris, which shows rather irregular morphology and kinematics, are similar to those in other nearby groups. Together with H I clouds recently detected near two other IC 1459 group members, namely IC 5270 and NGC 7418, using phased-array feeds on the Australian Square Kilometre Array Pathfinder, the detected debris make up a significant fraction of the group's intergalactic medium.

The two-point correlation function for groups of galaxies in the Center for Astrophysics redshift survey

NASA Technical Reports Server (NTRS)

Ramella, Massimo; Geller, Margaret J.; Huchra, John P.

1990-01-01

The large-scale distribution of groups of galaxies selected from complete slices of the CfA redshift survey extension is examined. The survey is used to reexamine the contribution of group members to the galaxy correlation function. The relationship between the correlation function for groups and those calculated for rich clusters is discussed, and the results for groups are examined as an extension of the relation between correlation function amplitude and richness. The group correlation function indicates that groups and individual galaxies are equivalent tracers of the large-scale matter distribution. The distribution of group centers is equivalent to random sampling of the galaxy distribution. The amplitude of the correlation function for groups is consistent with an extrapolation of the amplitude-richness relation for clusters. The amplitude scaled by the mean intersystem separation is also consistent with results for richer clusters.

Andromeda IV: A new local volume very metal-poor galaxy

NASA Astrophysics Data System (ADS)

Pustilnik, S. A.; Tepliakova, A. L.; Kniazev, A. Y.; Burenkov, A. N.

2008-06-01

And IV is a low surface brightness (LSB) dwarf galaxy at a distance of 6.1 Mpc, projecting close to M 31. In this paper the results of spectroscopy of the And IV two brightest HII regions with the SAO 6-m telescope (BTA) are presented. In spectra of both of them the faint line [OIII] λ4363 Å was detected and this allowed us to determine their O/H by the classical Te method. Their values for 12+log(O/H) are equal to 7.49±0.06 and 7.55±0.23, respectively. The comparison of the direct O/H calculations with the two most reliable semi-empirical and empirical methods shows the good consistency between these methods. For And IV absolute blue magnitude, MB = -12.6, our value for O/H corresponds to the ‘standard’ relation between O/H and LB for dwarf irregular galaxies (DIGs). And IV appears to be a new representative of the extremely metal-deficient gas-rich galaxies in the Local Volume. The very large range of M(HI) for LSB galaxies with close metallicities and luminosities indicates that simple models of LSBG chemical evolution are too limited to predict such striking diversity.

Ultracompact Blue Dwarfs: Galaxy Formation in the Local Universe?

NASA Astrophysics Data System (ADS)

Corbin, Michael

2004-07-01

Recent observations suggest that very low-mass galaxies in the local universe are still in the process of formation. To investigate this issue we propose to obtain deep ACS HRC images in the U, V and I bands of a sample of 11 "ultracompact" blue dwarf galaxies {UCBDs} identified in the Sloan Digital Sky Survey. These objects are nearby {z < 0.009}, actively star-forming, and have extremely small angular and physical sizes {d < 6" and D < 1 kpc}. They also tend to reside in voids. Our WFPC2 images of the prototype object of this class, POX 186, reveal this tiny object to have a highly disturbed morphlogy indicative of a recent {within 10^8 yr} collision between two small { 100 pc} clumps of stars that could represent the long-sought building blocks predicted by the Press-Schechter model of hierarchical galaxy formation. This collision has also triggered the formation of a "super" star cluster {SSC} at the object's core that may be the progenitor of a globular cluster. POX 186 thus appears to be a very small dwarf galaxy in the process of formation. This exciting discovery strongly motivates HST imaging of a full sample of UCBDs in order to determine if they have morphologies similar to POX 186. HST images are essential for resolving the structure of these objects, including establishing the presence of SSCs. HST also offers the only way to determine their morphologies in the near UV. The spectra of the objects available from the SDSS will also allow us to measure their star formation rates, dust content and metallicities. In addition to potentially providing the first direct evidence of Press-Schechter building blocks, these data could yield insight into the relationship between galaxy and globular cluster formation, and will serve as a test of the recent "downsizing" model of galaxy formation in which the least massive objects are the last to form.

Dwarf elliptical galaxies

NASA Technical Reports Server (NTRS)

Ferguson, Henry C.; Binggeli, Bruno

1994-01-01

Dwarf elliptical (dE) galaxies, with blue absolute magnitudes typically fainter than M(sub B) = -16, are the most numerous type of galaxy in the nearby universe. Tremendous advances have been made over the past several years in delineating the properties of both Local Group satellite dE's and the large dE populations of nearby clusters. We review some of these advances, with particular attention to how well currently availiable data can constrain (a) models for the formation of dE's, (b) the physical and evolutionary connections between different types of galaxies that overlap in the same portion of the mass-spectrum of galaxies, (c) the contribution of dE's to the galaxy luminosity functions in clusters and the field, (d) the star-forming histories of dE's and their possible contribution to faint galaxy counts, and (e) the clustering properties of dE's. In addressing these issues, we highlight the extent to which selection effects temper these constraints, and outline areas where new data would be particularly valuable.

Luminous Blue Compact Galaxies: Probes of galaxy assembly

NASA Astrophysics Data System (ADS)

Newton, Cassidy Louann

The life cycles of galaxies over cosmic time is yet to be fully understood. How did galaxies evolve from their formative stages to the structures we observe today? This dissertation details the identification and analysis of a sample of Luminous Blue Compact Galaxies (LBCGs), a class of galaxy in the local (z < 0.05) universe exhibiting blue colors, high surface brightness, and high star formation rates. These systems appear to be very similar in their global properties to the early evolutionary phases of most galaxies, however their locality permits detailed investigation over a broad range of the electromagnetic spectrum in contrast to the smaller angular sizes and extreme faintness of distant galaxies. We use a combination of optical, ultraviolet, and infrared data to investigate a sample of LBCGs utilizing space and ground-based data.

Intracluster medium cooling, AGN feedback, and brightest cluster galaxy properties of galaxy groups. Five properties where groups differ from clusters

NASA Astrophysics Data System (ADS)

Bharadwaj, V.; Reiprich, T. H.; Schellenberger, G.; Eckmiller, H. J.; Mittal, R.; Israel, H.

2014-12-01

Aims: We aim to investigate cool-core and non-cool-core properties of galaxy groups through X-ray data and compare them to the AGN radio output to understand the network of intracluster medium (ICM) cooling and feedback by supermassive black holes. We also aim to investigate the brightest cluster galaxies (BCGs) to see how they are affected by cooling and heating processes, and compare the properties of groups to those of clusters. Methods: Using Chandra data for a sample of 26 galaxy groups, we constrained the central cooling times (CCTs) of the ICM and classified the groups as strong cool-core (SCC), weak cool-core (WCC), and non-cool-core (NCC) based on their CCTs. The total radio luminosity of the BCG was obtained using radio catalogue data and/or literature, which in turn was compared to the cooling time of the ICM to understand the link between gas cooling and radio output. We determined K-band luminosities of the BCG with 2MASS data, and used a scaling relation to constrain the masses of the supermassive black holes, which were then compared to the radio output. We also tested for correlations between the BCG luminosity and the overall X-ray luminosity and mass of the group. The results obtained for the group sample were also compared to previous results for clusters. Results: The observed cool-core/non-cool-core fractions for groups are comparable to those of clusters. However, notable differences are seen: 1) for clusters, all SCCs have a central temperature drop, but for groups this is not the case as some have centrally rising temperature profiles despite very short cooling times; 2) while for the cluster sample, all SCC clusters have a central radio source as opposed to only 45% of the NCCs, for the group sample, all NCC groups have a central radio source as opposed to 77% of the SCC groups; 3) for clusters, there are indications of an anticorrelation trend between radio luminosity and CCT. However, for groups this trend is absent; 4) the indication of

Galaxy-Galaxy Lensing in the Hubble Deep Field: The Halo Tully-Fisher Relation at Intermediate Redshift

NASA Astrophysics Data System (ADS)

Hudson, Michael J.; Gwyn, Stephen D. J.; Dahle, Håkon; Kaiser, Nick

1998-08-01

A tangential distortion of background source galaxies around foreground lens galaxies in the Hubble Deep Field is detected at the 99.3% confidence level. An important element of our analysis is the use of photometric redshifts to determine distances of lens and source galaxies and rest-frame B-band luminosities of the lens galaxies. The lens galaxy halos obey a Tully-Fisher relation between halo circular velocity and luminosity. The typical lens galaxy, at a redshift z = 0.6, has a circular velocity of 210 +/- 40 km s-1 at MB = -18.5, if q0 = 0.5. Control tests, in which lens and source positions and source ellipticities are randomized, confirm the significance level of the detection quoted above. Furthermore, a marginal signal is also detected from an independent, fainter sample of source galaxies without photometric redshifts. Potential systematic effects, such as contamination by aligned satellite galaxies, the distortion of source shapes by the light of the foreground galaxies, PSF anisotropies, and contributions from mass distributed on the scale of galaxy groups are shown to be negligible. A comparison of our result with the local Tully-Fisher relation indicates that intermediate-redshift galaxies are fainter than local spirals by 1.0 +/- 0.6 B mag at a fixed circular velocity. This is consistent with some spectroscopic studies of the rotation curves of intermediate-redshift galaxies. This result suggests that the strong increase in the global luminosity density with redshift is dominated by evolution in the galaxy number density.

The Complete Local Volume Groups Sample - I. Sample selection and X-ray properties of the high-richness subsample

NASA Astrophysics Data System (ADS)

O'Sullivan, Ewan; Ponman, Trevor J.; Kolokythas, Konstantinos; Raychaudhury, Somak; Babul, Arif; Vrtilek, Jan M.; David, Laurence P.; Giacintucci, Simona; Gitti, Myriam; Haines, Chris P.

2017-12-01

We present the Complete Local-Volume Groups Sample (CLoGS), a statistically complete optically selected sample of 53 groups within 80 Mpc. Our goal is to combine X-ray, radio and optical data to investigate the relationship between member galaxies, their active nuclei and the hot intra-group medium (IGM). We describe sample selection, define a 26-group high-richness subsample of groups containing at least four optically bright (log LB ≥ 10.2 LB⊙) galaxies, and report the results of XMM-Newton and Chandra observations of these systems. We find that 14 of the 26 groups are X-ray bright, possessing a group-scale IGM extending at least 65 kpc and with luminosity >1041 erg s-1, while a further three groups host smaller galaxy-scale gas haloes. The X-ray bright groups have masses in the range M500 ≃ 0.5-5 × 1013 M⊙, based on system temperatures of 0.4-1.4 keV, and X-ray luminosities in the range 2-200 × 1041 erg s-1. We find that ∼53-65 per cent of the X-ray bright groups have cool cores, a somewhat lower fraction than found by previous archival surveys. Approximately 30 per cent of the X-ray bright groups show evidence of recent dynamical interactions (mergers or sloshing), and ∼35 per cent of their dominant early-type galaxies host active galactic nuclei with radio jets. We find no groups with unusually high central entropies, as predicted by some simulations, and confirm that CLoGS is in principle capable of detecting such systems. We identify three previously unrecognized groups, and find that they are either faint (LX, R500 < 1042 erg s-1) with no concentrated cool core, or highly disturbed. This leads us to suggest that ∼20 per cent of X-ray bright groups in the local universe may still be unidentified.

Understanding the scatter in the spatially resolved star formation main sequence of local massive spiral galaxies

NASA Astrophysics Data System (ADS)

Abdurro'uf; Akiyama, Masayuki

2017-08-01

We investigate the relation between star formation rate (SFR) and stellar mass (M*) at the sub-galactic scale (˜1 kpc) of 93 local (0.01 < z < 0.02) massive (M* > 1010.5 M⊙) spiral galaxies. To derive a spatially resolved SFR and stellar mass, we perform the so-called pixel-to-pixel spectral energy distribution (SED) fitting, which fits an observed spatially resolved multiband SED with a library of model SEDs using Bayesian statistics. We use two bands (far-ultraviolet or FUV and near-ultraviolet or NUV) and five bands (u, g, r, I and z) of imaging data from Galaxy Evolution Explorer (GALEX) and Sloan Digital Sky Survey (SDSS), respectively. We find a tight nearly linear relation between the local surface density of SFR (ΣSFR) and stellar mass (Σ*), which is flattened at high Σ*. The near linear relation between Σ* and ΣSFR suggests a constant specific SFR (sSFR) throughout the galaxies, and the scatter of the relation is directly related to that of the sSFR. Therefore, we analyse the variation of the sSFR in various scales. More massive galaxies on average have lower sSFR throughout them than less massive galaxies. We also find that barred galaxies have a lower sSFR in the core region than non-barred galaxies. However, in the outer region, the sSFRs of barred and non-barred galaxies are similar and lead to a similar total sSFR.

Herschel observations of Hickson compact groups of galaxies: Unveiling the properties of cold dust

NASA Astrophysics Data System (ADS)

Bitsakis, T.; Charmandaris, V.; Appleton, P. N.; Díaz-Santos, T.; Le Floc'h, E.; da Cunha, E.; Alatalo, K.; Cluver, M.

2014-05-01

We present a Herschel far-infrared and sub-millimetre (sub-mm) study of a sample of 120 galaxies in 28 Hickson compact groups (HCGs). Fitting their UV to sub-mm spectral energy distributions with the model of da Cunha et al. (2008), we accurately estimate the dust masses, luminosities, and temperatures of the individual galaxies. We find that nearly half of the late-type galaxies in dynamically "old" groups, those with more than 25% of early-type members and redder UV-optical colours, also have significantly lower dust-to-stellar mass ratios compared to those of actively star-forming galaxies of the same mass found both in HCGs and in the field. Examining their dust-to-gas mass ratios, we conclude that dust was stripped out of these systems as a result of the gravitational and hydrodynamic interactions, experienced owing to previous encounters with other group members. About 40% of the early-type galaxies (mostly lenticulars), in dynamically "old" groups, display dust properties similar to those of the UV-optical red late-type galaxies. Given their stellar masses, star formation rates, and UV-optical colours, we suggest that red late-type and dusty lenticular galaxies represent transition populations between blue star-forming disk galaxies and quiescent early-type ellipticals. On the other hand, both the complete absence of any correlation between the dust and stellar masses of the dusty ellipticals and their enhanced star formation activity, suggest the increase in their gas and dust content due to accretion and merging. Our deep Herschel observations also allow us to detect the presence of diffuse cold intragroup dust in 4 HCGs. We also find that the fraction of 250 μm emission that is located outside of the main bodies of both the red late-type galaxies and the dusty lenticulars is 15-20% of their integrated emission at this band. All these findings are consistent with an evolutionary scenario in which gas dissipation, shocks, and turbulence, in addition to

The evolution of massive stars: bridging the gap in the Local Group.

PubMed

Massey, Philip; Neugent, Kathryn F; Levesque, Emily M

2017-10-28

The nearby galaxies of the Local Group can act as our laboratories in helping to bridge the gap between theory and observations. In this review, we will describe the complications of identifying samples of OB stars, yellow and red supergiants, and Wolf-Rayet stars, and what we have so far learned from these studies.This article is part of the themed issue 'Bridging the gap: from massive stars to supernovae'. © 2017 The Author(s).

Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deason, Alis; Wetzel, Andrew; Garrison-Kimmel, Shea, E-mail: alis@ucolick.org

Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M {sub star} > 10{sup 6} M {sub ☉} that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with amore » lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.« less

Chemical evolution of Local Group dwarf galaxies in a cosmological context - I. A new modelling approach and its application to the Sculptor dwarf spheroidal galaxy

NASA Astrophysics Data System (ADS)

Romano, Donatella; Starkenburg, Else

2013-09-01

We present a new approach for chemical evolution modelling, specifically designed to investigate the chemical properties of dwarf galaxies in a full cosmological framework. In particular, we focus on the Sculptor dwarf spheroidal galaxy, for which a wealth of observational data exists, as a test bed for our model. We select four candidate Sculptor-like galaxies from the satellite galaxy catalogue generated by implementation of a version of the Munich semi-analytic model for galaxy formation on the level 2 Aquarius dark matter simulations and use the mass assembly and star formation histories predicted for these four systems as an input for the chemical evolution code. We follow explicitly the evolution of several chemical elements, both in the cold gas out of which the stars form and in the hot medium residing in the halo. We take into account in detail the lifetimes of stars of different initial masses, the distribution of the delay times for Type Ia supernova explosions and the dependence of the stellar yields from the initial metallicity of the stars. We allow large fractions of metals to be deposited into the hot phase, either directly as stars die or through reheated gas flows powered by supernova explosions. We find that, in order to reproduce both the observed metallicity distribution function and the observed abundance ratios of long-lived stars of Sculptor, large fractions of the reheated metals must never re-enter regions of active star formation. With this prescription, all the four analogues to the Sculptor dwarf spheroidal galaxy extracted from the simulated satellites catalogue on the basis of luminosity and stellar population ages are found to reasonably match the detailed chemical properties of real Sculptor stars. However, all model galaxies do severely underestimate the fraction of very metal poor stars observed in Sculptor. Our analysis thus sets further constraints on the semi-analytical models and, at large, on possible metal enrichment

The Next Generation Virgo Cluster Survey. VII. The Intrinsic Shapes of Low-luminosity Galaxies in the Core of the Virgo Cluster, and a Comparison with the Local Group

NASA Astrophysics Data System (ADS)

Sánchez-Janssen, Rubén; Ferrarese, Laura; MacArthur, Lauren A.; Côté, Patrick; Blakeslee, John P.; Cuillandre, Jean-Charles; Duc, Pierre-Alain; Durrell, Patrick; Gwyn, Stephen; McConnacchie, Alan W.; Boselli, Alessandro; Courteau, Stéphane; Emsellem, Eric; Mei, Simona; Peng, Eric; Puzia, Thomas H.; Roediger, Joel; Simard, Luc; Boyer, Fred; Santos, Matthew

2016-03-01

We investigate the intrinsic shapes of low-luminosity galaxies in the central 300 kpc of the Virgo Cluster using deep imaging obtained as part of the Next Generation Virgo Cluster Survey (NGVS). We build a sample of nearly 300 red-sequence cluster members in the yet-unexplored -14 < Mg < -8 mag range, and we measure their apparent axis ratios, q, through Sérsic fits to their two-dimensional light distribution, which is well described by a constant ellipticity parameter. The resulting distribution of apparent axis ratios is then fit by families of triaxial models with normally distributed intrinsic ellipticities, E = 1 - C/A, and triaxialities, T = (A2 - B2)/(A2 - C2). We develop a Bayesian framework to explore the posterior distribution of the model parameters, which allows us to work directly on discrete data, and to account for individual, surface-brightness-dependent axis ratio uncertainties. For this population we infer a mean intrinsic ellipticity \\bar{E} = {0.43}-0.02+0.02 and a mean triaxiality \\bar{T} = {0.16}-0.06+0.07. This implies that faint Virgo galaxies are best described as a family of thick, nearly oblate spheroids with mean intrinsic axis ratios 1:0.94:0.57. The core of Virgo lacks highly elongated low-luminosity galaxies, with 95% of the population having q > 0.45. We additionally attempt a study of the intrinsic shapes of Local Group (LG) satellites of similar luminosities. For the LG population we infer a slightly larger mean intrinsic ellipticity \\bar{E} = {0.51}-0.06+0.07, and the paucity of objects with round apparent shapes translates into more triaxial mean shapes, 1:0.76:0.49. Numerical studies that follow the tidal evolution of satellites within LG-sized halos are in good agreement with the inferred shape distributions, but the mismatch for faint galaxies in Virgo highlights the need for more adequate simulations of this population in the cluster environment. We finally compare the intrinsic shapes of NGVS low-mass galaxies with

The Carnegie-Chicago Hubble Program: Discovery of the Most Distant Ultra-faint Dwarf Galaxy in the Local Universe

NASA Astrophysics Data System (ADS)

Lee, Myung Gyoon; Jang, In Sung; Beaton, Rachael; Seibert, Mark; Bono, Giuseppe; Madore, Barry

2017-02-01

Ultra-faint dwarf galaxies (UFDs) are the faintest known galaxies, and due to their incredibly low surface brightness, it is difficult to find them beyond the Local Group. We report a serendipitous discovery of a UFD, Fornax UFD1, in the outskirts of NGC 1316, a giant galaxy in the Fornax cluster. The new galaxy is located at a projected radius of 55 kpc in the south-east of NGC 1316. This UFD is found as a small group of resolved stars in the Hubble Space Telescope images of a halo field of NGC 1316, obtained as part of the Carnegie-Chicago Hubble Program. Resolved stars in this galaxy are consistent with being mostly metal-poor red giant branch (RGB) stars. Applying the tip of the RGB method to the mean magnitude of the two brightest RGB stars, we estimate the distance to this galaxy, 19.0 ± 1.3 Mpc. Fornax UFD1 is probably a member of the Fornax cluster. The color-magnitude diagram of these stars is matched by a 12 Gyr isochrone with low metallicity ([Fe/H] ≈ -2.4). Total magnitude and effective radius of Fornax UFD1 are MV ≈ -7.6 ± 0.2 mag and reff = 146 ± 9 pc, which are similar to those of Virgo UFD1 that was discovered recently in the intracluster field of Virgo by Jang & Lee. Fornax UFD1 is the most distant known UFD that is confirmed by resolved stars. This indicates that UFDs are ubiquitous and that more UFDs remain to be discovered in the Fornax cluster. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #10505 and #13691.

A new method for finding and characterizing galaxy groups via low-frequency radio surveys

NASA Astrophysics Data System (ADS)

Croston, J. H.; Ineson, J.; Hardcastle, M. J.; Mingo, B.

2017-09-01

We describe a new method for identifying and characterizing the thermodynamic state of large samples of evolved galaxy groups at high redshifts using high-resolution, low-frequency radio surveys, such as those that will be carried out with LOFAR and the Square Kilometre Array. We identify a sub-population of morphologically regular powerful [Fanaroff-Riley type II (FR II)] radio galaxies and demonstrate that, for this sub-population, the internal pressure of the radio lobes is a reliable tracer of the external intragroup/intracluster medium (ICM) pressure, and that the assumption of a universal pressure profile for relaxed groups enables the total mass and X-ray luminosity to be estimated. Using a sample of well-studied FR II radio galaxies, we demonstrate that our method enables the estimation of group/cluster X-ray luminosities over three orders of magnitude in luminosity to within a factor of ˜2 from low-frequency radio properties alone. Our method could provide a powerful new tool for building samples of thousands of evolved galaxy groups at z > 1 and characterizing their ICM.

Killing Star Formation in Satellite Galaxies

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-08-01

When a dwarf galaxy falls into the halo of a large galaxy like the Milky Way, how is star formation in the dwarf affected? A collaboration led by Andrew Wetzel (California Institute of Technology and Carnegie Observatories) recently set out to answer this question using observations of nearby galaxies and simulations of the infall process. Observed Quenching: Isolated dwarf galaxies tend to be gas-rich and very actively star-forming. In contrast, most dwarf galaxies within 300 kpc of us (the Milky Way's virial radius) contain little or no cold gas, and they're quiescent: there's not much star formation happening. And this isn't just true of the Milky Way; we observe the same difference in the satellite galaxies surrounding Andromeda galaxy. Once a dwarf galaxy has moved into the gravitational realm of a larger galaxy, the satellite's gas vanishes rapidly and its star formation is shut off — but how, and on what timescale? The known dwarf galaxies in the Local Group (out to 1.6 Mpc) are plotted by their distance from their host vs. their stellar mass. Blue stars indicate actively star-forming dwarfs and red circles indicate quiescent ones. Credit: Wetzel et al. 2015. Timescales for Quiescence: To answer these questions, the authors explored the process of galaxy infall using Exploring the Local Volume in Simulations (ELVIS), a suite of cosmological N-body simulations intended to explore the Local Group. They combined the infall times from the simulations with observational knowledge of the fraction of nearby galaxies that are currently quiescent, in order to determine what timescales are required for different processes to deplete the gas in the dwarf galaxies and quench star formation. Based on their results, two types of quenching culprits are at work: gas consumption (where a galaxy simply uses up its immediate gas supply and doesn't have access to more) and gas stripping (where external forces like ram pressure remove gas from the galaxy). These processes

ECO and RESOLVE: Galaxy Disk Growth in Environmental Context

NASA Astrophysics Data System (ADS)

Moffett, Amanda J.; Kannappan, Sheila J.; Berlind, Andreas A.; Eckert, Kathleen D.; Stark, David V.; Hendel, David; Norris, Mark A.; Grogin, Norman A.

2015-10-01

We study the relationships between galaxy environments and galaxy properties related to disk (re)growth, considering two highly complete samples that are approximately baryonic mass limited into the high-mass dwarf galaxy regime, the Environmental COntext catalog (data release herein) and the B-semester region of the REsolved Spectroscopy Of a Local VolumE survey. We quantify galaxy environments using both group identification and smoothed galaxy density field methods. We use by-eye and quantitative morphological classifications plus atomic gas content measurements and estimates. We find that blue early-type (E/S0) galaxies, gas-dominated galaxies, and UV-bright disk host galaxies all become distinctly more common below group halo mass ˜ {10}11.5 {M}⊙ , implying that this low group halo mass regime may be a preferred regime for significant disk growth activity. We also find that blue early-type and blue late-type galaxies inhabit environments of similar group halo mass at fixed baryonic mass, consistent with a scenario in which blue early-types can regrow late-type disks. In fact, we find that the only significant difference in the typical group halo mass inhabited by different galaxy classes is for satellite galaxies with different colors, where at fixed baryonic mass red early- and late-types have higher typical group halo masses than blue early- and late-types. More generally, we argue that the traditional morphology-environment relation (i.e., that denser environments tend to have more early-types) can be largely attributed to the morphology-galaxy mass relation for centrals and the color-environment relation for satellites.

CO in Hickson compact group galaxies with enhanced warm H2 emission: Evidence for galaxy evolution?

NASA Astrophysics Data System (ADS)

Lisenfeld, U.; Appleton, P. N.; Cluver, M. E.; Guillard, P.; Alatalo, K.; Ogle, P.

2014-10-01

Context. Galaxies in Hickson Compact Groups (HCGs) are believed to experience morphological transformations from blue, star-forming galaxies to red, early-type galaxies. Galaxies with a high ratio between the luminosities of the warm H2 to the 7.7 μm PAH emission (so-called Molecular Hydrogen Emission Galaxies, MOHEGs) are predominantly in an intermediate phase, the green valley. Their enhanced H2 emission suggests that the molecular gas is affected in the transition. Aims: We study the properties of the molecular gas traced by CO in galaxies in HCGs with measured warm H2 emission in order to look for evidence of the perturbations affecting the warm H2 in the kinematics, morphology and mass of the molecular gas. Methods: We observed the CO(1-0) emission of 20 galaxies in HCGs and complemented our sample with 11 CO(1-0) spectra from the literature. Most of the galaxies have measured warm H2 emission, and 14 of them are classified as MOHEGs. We mapped some of these galaxies in order to search for extra-galactic CO emission. We analyzed the molecular gas mass derived from CO(1-0), MH2, and its kinematics, and then compared it to the mass of the warm molecular gas, the stellar mass and star formation rate (SFR). Results: Our results are the following. (i) The mass ratio between the CO-derived and the warm H2 molecular gas is in the same range as found for field galaxies. (ii) Some of the galaxies, mostly MOHEGs, have very broad CO linewidths of up to 1000 km s-1 in the central pointing. The line shapes are irregular and show various components. (iii) In the mapped objects we found asymmetric distributions of the cold molecular gas. (iv) The star formation efficiency (=SFR/MH2) of galaxies in HCGs is very similar to isolated galaxies. No significant difference between MOHEGs and non-MOHEGs or between early-type and spiral galaxies has been found. In a few objects the SFE is significantly lower, indicating the presence of molecular gas that is not actively forming stars

Optical-to-virial velocity ratios of local disc galaxies from combined kinematics and galaxy-galaxy lensing

NASA Astrophysics Data System (ADS)

Reyes, R.; Mandelbaum, R.; Gunn, J. E.; Nakajima, R.; Seljak, U.; Hirata, C. M.

2012-10-01

In this paper, we measure the optical-to-virial velocity ratios Vopt/V200c of disc galaxies in the Sloan Digital Sky Survey (SDSS) at a mean redshift of = 0.07 and with stellar masses 109 < M* < 1011 M⊙. Vopt/V200c, the ratio of the circular velocity measured at the optical radius of the disc (˜10 kpc) to that at the virial radius of the dark matter halo (˜150 kpc), is a powerful observational constraint on disc galaxy formation. It links galaxies to their dark matter haloes dynamically and constrains the total mass profile of disc galaxies over an order of magnitude in length scale. For this measurement, we combine Vopt derived from the Tully-Fisher relation (TFR) from Reyes et al. with V200c derived from halo masses measured with galaxy-galaxy lensing. In anticipation of this combination, we use similarly selected galaxy samples for both the TFR and lensing analysis. For three M* bins with lensing-weighted mean stellar masses of 0.6, 2.7 and 6.5 × 1010 M⊙, we find halo-to-stellar mass ratios M200c/M* = 41, 23 and 26, with 1σ statistical uncertainties of around 0.1 dex, and Vopt/V200c = 1.27 ± 0.08, 1.39 ± 0.06 and 1.27 ± 0.08 (1σ), respectively. Our results suggest that the dark matter and baryonic contributions to the mass within the optical radius are comparable, if the dark matter halo profile has not been significantly modified by baryons. The results obtained in this work will serve as inputs to and constraints on disc galaxy formation models, which will be explored in future work. Finally, we note that this paper presents a new and improved galaxy shape catalogue for weak lensing that covers the full SDSS Data Release 7 footprint.

Do galaxy global relationships emerge from local ones? The SDSS IV MaNGA surface mass density-metallicity relation

NASA Astrophysics Data System (ADS)

Barrera-Ballesteros, Jorge K.; Heckman, Timothy M.; Zhu, Guangtun B.; Zakamska, Nadia L.; Sánchez, Sebastian F.; Law, David; Wake, David; Green, Jenny E.; Bizyaev, Dmitry; Oravetz, Daniel; Simmons, Audrey; Malanushenko, Elena; Pan, Kaike; Roman Lopes, Alexandre; Lane, Richard R.

2016-12-01

We present the stellar surface mass density versus gas metallicity (Σ*-Z) relation for more than 500 000 spatially resolved star-forming resolution elements (spaxels) from a sample of 653 disc galaxies included in the SDSS IV MaNGA survey. We find a tight relation between these local properties, with higher metallicities as the surface density increases. This relation extends over three orders of magnitude in the surface mass density and a factor of 4 in metallicity. We show that this local relationship can simultaneously reproduce two well-known properties of disc galaxies: their global mass-metallicity relationship and their radial metallicity gradients. We also find that the Σ*-Z relation is largely independent of the galaxy's total stellar mass and specific star formation rate (sSFR), except at low stellar mass and high sSFR. These results suggest that in the present-day universe local properties play a key role in determining the gas-phase metallicity in typical disc galaxies.

WHERE DO WET, DRY, AND MIXED GALAXY MERGERS OCCUR? A STUDY OF THE ENVIRONMENTS OF CLOSE GALAXY PAIRS IN THE DEEP2 GALAXY REDSHIFT SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Lihwai; Cooper, Michael C.; Willmer, Christopher N. A.

2010-08-01

We study the environments of wet, dry, and mixed galaxy mergers at 0.75 < z < 1.2 using close pairs in the DEEP2 Galaxy Redshift Survey. We find that the typical environment of dry and mixed merger candidates is denser than that of wet mergers, mostly due to the color-density relation. While the galaxy companion rate (N{sub c}) is observed to increase with overdensity, using N-body simulations, we find that the fraction of pairs that will eventually merge decreases with the local density, predominantly because interlopers are more common in dense environments. After taking into account the merger probability ofmore » pairs as a function of local density, we find only marginal environment dependence of the galaxy merger rate for wet mergers. On the other hand, the dry and mixed merger rates increase rapidly with local density due to the increased population of red galaxies in dense environments, implying that the dry and mixed mergers are most effective in overdense regions. We also find that the environment distribution of K+A galaxies is similar to that of wet mergers alone and of wet+mixed mergers, suggesting a possible connection between K+A galaxies and wet and/or wet+mixed mergers. Based on our results, we therefore expect that the properties, including structures and masses, of red-sequence galaxies should be different between those in underdense regions and those in overdense regions since the dry mergers are significantly more important in dense environments. We conclude that, as early as z {approx} 1, high-density regions are the preferred environment in which dry mergers occur, and that present-day red-sequence galaxies in overdense environments have, on average, undergone 1.2 {+-} 0.3 dry mergers since this time, accounting for (38 {+-} 10)% of their mass accretion in the last 8 billion years. The main uncertainty in this finding is the conversion from the pair fraction to the galaxy merger rate, which is possibly as large as a factor of 2. Our

The Star Formation History of the Local Group Dwarf Galaxy Leo I

NASA Astrophysics Data System (ADS)

Gallart, Carme; Freedman, Wendy L.; Aparicio, Antonio; Bertelli, Giampaolo; Chiosi, Cesare

1999-11-01

We present a quantitative analysis of the star formation history (SFH) of the Local Group dSph galaxy Leo I, from the information in its Hubble Space Telescope [(V-I),I] color-magnitude diagram (CMD). It reaches the level of the oldest main-sequence turnoffs, and this allows us to retrieve the SFH in considerable detail. The method we use is based on comparing, via synthetic CMDs, the expected distribution of stars in the CMD for different evolutionary scenarios with the observed distribution. We consider the SFH to be composed by the SFR(t), the chemical enrichment law Z(t), the initial mass function (IMF), and a function β(f,q) controlling the fraction f and mass ratio distribution q of binary stars. We analyze a set of ~=50 combinations of four Z(t), three IMFs, and more than four β(f,q). For each of them, the best SFR(t) is searched for among ~=6x107 models. The comparison between the observed CMD and the model CMDs is done through χ2ν minimization of the differences in the number of stars in a set of regions of the CMD, chosen to sample stars of different ages or in specific stellar evolutionary phases. We empirically determine the range of χ2ν values that indicate acceptable models for our set of data using tests with models with known SFHs. Our solution for the SFH of Leo I defines a minimum of χ2ν in a well-defined position of the parameter space, and the derived SFR(t) is robust, in the sense that its main characteristics are unchanged for different combinations of the remaining parameters. However, only a narrow range of assumptions for Z(t), IMF, and β(f,q) result in a good agreement between the data and the models, namely, Z=0.0004, a IMF Kroupa et al. or slightly steeper, and a relatively large fraction of binary stars, with f=0.3-0.6, q>0.6, and an approximately flat IMF for the secondaries, or particular combinations of these parameters that would produce a like fraction of similar mass binaries. Most star formation activity (70% to 80

RR Lyrae in the UMi dSph Galaxy

NASA Astrophysics Data System (ADS)

Kuehn, Charles; Kinemuchi, Karen; Jeffery, Elizabeth; Grabowski, Kathleen; Nemec, James; Herrera, Daniel

2018-01-01

Over the past two years we have obtained observations of the Ursa Minor dwarf spheroidal galaxy with the goal of completing an updated catalog of the variable stars in the dwarf galaxy. In addition to finding new variable stars, this updated catalog will allow us to look at period changes in the variables and to determine stellar characteristic for the RR Lyrae stars in the dSph. We will compare the RR Lyrae stellar characteristics to other RR Lyrae stars found in the Local Group dSph galaxies; these comparisons can give us insights to the near-field cosmology of the Local Group. In this poster we present our updated catalog of RR Lyrae stars in the UMi dSph; the updated catalog includes Fourier decomposition parameters, metallicities, and other physical properties for the RR Lyrae stars.

Star Formation in Undergraduate ALFALFA Team Galaxy Groups and Clusters

NASA Astrophysics Data System (ADS)

Koopmann, Rebecca A.; Durbala, Adriana; Finn, Rose; Haynes, Martha P.; Coble, Kimberly A.; Craig, David W.; Hoffman, G. Lyle; Miller, Brendan P.; Crone-Odekon, Mary; O'Donoghue, Aileen A.; Troischt, Parker; Undergraduate ALFALFA Team; ALFALFA Team

2017-01-01

The Undergraduate ALFALFA Team (UAT) Groups project is a coordinated study of gas and star formation properties of galaxies in and around 36 nearby (z<0.03) groups and clusters of varied richness, morphological type mix, and X-ray luminosity. By studying a large range of environments and considering the spatial distributions of star formation, we probe mechanisms of gas depletion and morphological transformation. The project uses ALFALFA HI observations, optical observations, and digital databases like SDSS, and incorporates work undertaken by faculty and students at different institutions within the UAT. Here we present results from our wide area Hα and broadband R imaging project carried out with the WIYN 0.9m+MOSAIC/HDI at KPNO, including an analysis of radial star formation rates and extents of galaxies in the NGC 5846, Abell 779, NRGb331, and HCG 69 groups/clusters. This work has been supported by NSF grant AST-1211005 and AST-1637339.

Understanding Local Luminous Infrared Galaxies in the Herschel Era

NASA Astrophysics Data System (ADS)

Chu, Jason; Sanders, David B.; Larson, Kirsten L.; Mazzarella, Joseph M.; Howell, Justin; Diaz Santos, Tanio; Xu, C. Kevin; Paladini, Roberta; Schulz, Bernhard; Shupe, David L.; Appleton, Philip N.; Armus, Lee; Billot, Nicolas; Pan Chan, Hiu; Evans, Aaron S.; Fadda, Dario; Frayer, David T.; Haan, Sebastian; Mie Ishida, Catherine; Iwasawa, Kazushi; Kim, Dong-Chan; Lord, Steven D.; Murphy, Eric J.; Petric, Andreea; Privon, George C.; Surace, Jason A.; Treister, Ezequiel; Great Observatories All-Sky LIRG Survey, Cosmic Evolution Survey

2017-06-01

Luminous and ultraluminous infrared galaxies [(U)LIRGs] are some of the most extreme objects in the universe with their elevated star formation rates and/or presence of a powerful AGN, playing a central role in the evolution of galaxies throughout cosmic history. The 201 local (U)LIRGs (z<0.088) within the Great Observatories All-Sky LIRG Survey (GOALS) provide an unmatched opportunity to characterize the diverse properties in a large, statistically significant sample, in addition to comparisons with their high redshift counterparts. In this thesis talk I will first present the Herschel PACS and SPIRE far infrared image atlas of the entire GOALS sample (encompassing the 70-500 micron wavelength range), and demonstrate the excellent data quality. The Herschel GOALS images presented here are the highest resolution, most sensitive and comprehensive far-infrared imaging survey of the nearest (U)LIRGs to date. This allows us for the first time to directly probe the critical far infrared and submillimeter wavelength regime of these systems, enabling us to accurately determine the bolometric luminosities, infrared surface brightnesses, star formation rates, and dust masses and temperatures on spatial scales of 2-5 kpc. In addition, the superb resolution of Herschel means we can resolve many of the galaxy pairs and systems within the GOALS sample, allowing us to measure far infrared fluxes of component galaxies. Finally, using the Herschel photometry in conjunction with Spitzer, WISE, and IRAS data, I will show our first results on the global properties of (U)LIRGs such as their average 3-500 micron infrared SEDs and far infrared colors, and compare them to lower infrared luminosity objects. We will also compare and contrast their infrared SED shapes with previously published SED templates from the literature. If time permits, I will also show initial results from our rest-frame optical spectroscopy program on z~2.3 infrared selected galaxies in the COSMOS field.

Photometry of resolved galaxies. IV - Holmberg I and Holmberg II

NASA Technical Reports Server (NTRS)

Hoessel, J. G.; Danielson, G. E.

1984-01-01

Colors and magnitudes are presented for 279 resolved stars in the Holmberg I dwarf galaxy and 468 resolved stars in Holmberg II. Both systems are Magellanic type dwarf members of the M81-NGC 2403 Group, which lies at approximately 3 Mpc from the Local Group. The photometry was done in the GRI passbands using CCD detectors. Color-magnitude diagrams and luminosity functions are constructed; these are compared with results for several Local Group galaxies and with theoretical work. Holmberg I is found to have a low present star formation rate, while Holmberg II is very active at present.

GRB 080517: a local, low-luminosity gamma-ray burst in a dusty galaxy at z = 0.09

NASA Astrophysics Data System (ADS)

Stanway, Elizabeth R.; Levan, Andrew J.; Tanvir, Nial; Wiersema, Klaas; van der Horst, Alexander; Mundell, Carole G.; Guidorzi, Cristiano

2015-02-01

We present an analysis of the photometry and spectroscopy of the host galaxy of Swift-detected GRB 080517. From our optical spectroscopy, we identify a redshift of z = 0.089 ± 0.003, based on strong emission lines, making this a rare example of a very local, low-luminosity, long gamma-ray burst. The galaxy is detected in the radio with a flux density of S4.5 GHz = 0.22 ± 0.04 mJy - one of relatively few known gamma-ray bursts hosts with a securely measured radio flux. Both optical emission lines and a strong detection at 22 μm suggest that the host galaxy is forming stars rapidly, with an inferred star formation rate ˜16 M⊙ yr-1 and a high dust obscuration (E(B - V) > 1, based on sightlines to the nebular emission regions). The presence of a companion galaxy within a projected distance of 25 kpc, and almost identical in redshift, suggests that star formation may have been triggered by galaxy-galaxy interaction. However, fitting of the remarkably flat spectral energy distribution from the ultraviolet through to the infrared suggests that an older, 500 Myr post-starburst stellar population is present along with the ongoing star formation. We conclude that the host galaxy of GRB 080517 is a valuable addition to the still very small sample of well-studied local gamma-ray burst hosts.

Constraints on the optical depth of galaxy groups and clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flender, Samuel; Nagai, Daisuke; McDonald, Michael

Here, future data from galaxy redshift surveys, combined with high-resolutions maps of the cosmic microwave background, will enable measurements of the pairwise kinematic Sunyaev–Zel'dovich (kSZ) signal with unprecedented statistical significance. This signal probes the matter-velocity correlation function, scaled by the average optical depth (τ) of the galaxy groups and clusters in the sample, and is thus of fundamental importance for cosmology. However, in order to translate pairwise kSZ measurements into cosmological constraints, external constraints on τ are necessary. In this work, we present a new model for the intracluster medium, which takes into account star formation, feedback, non-thermal pressure, and gas cooling. Our semi-analytic model is computationally efficient and can reproduce results of recent hydrodynamical simulations of galaxy cluster formation. We calibrate the free parameters in the model using recent X-ray measurements of gas density profiles of clusters, and gas masses of groups and clusters. Our observationally calibrated model predicts the averagemore » $${\\tau }_{500}$$ (i.e., the integrated τ within a disk of size R 500) to better than 6% modeling uncertainty (at 95% confidence level). If the remaining uncertainties associated with other astrophysical uncertainties and X-ray selection effects can be better understood, our model for the optical depth should break the degeneracy between optical depth and cluster velocity in the analysis of future pairwise kSZ measurements and improve cosmological constraints with the combination of upcoming galaxy and CMB surveys, including the nature of dark energy, modified gravity, and neutrino mass.« less

Constraints on the optical depth of galaxy groups and clusters

DOE PAGES

Flender, Samuel; Nagai, Daisuke; McDonald, Michael

2017-03-10

Here, future data from galaxy redshift surveys, combined with high-resolutions maps of the cosmic microwave background, will enable measurements of the pairwise kinematic Sunyaev–Zel'dovich (kSZ) signal with unprecedented statistical significance. This signal probes the matter-velocity correlation function, scaled by the average optical depth (τ) of the galaxy groups and clusters in the sample, and is thus of fundamental importance for cosmology. However, in order to translate pairwise kSZ measurements into cosmological constraints, external constraints on τ are necessary. In this work, we present a new model for the intracluster medium, which takes into account star formation, feedback, non-thermal pressure, and gas cooling. Our semi-analytic model is computationally efficient and can reproduce results of recent hydrodynamical simulations of galaxy cluster formation. We calibrate the free parameters in the model using recent X-ray measurements of gas density profiles of clusters, and gas masses of groups and clusters. Our observationally calibrated model predicts the averagemore » $${\\tau }_{500}$$ (i.e., the integrated τ within a disk of size R 500) to better than 6% modeling uncertainty (at 95% confidence level). If the remaining uncertainties associated with other astrophysical uncertainties and X-ray selection effects can be better understood, our model for the optical depth should break the degeneracy between optical depth and cluster velocity in the analysis of future pairwise kSZ measurements and improve cosmological constraints with the combination of upcoming galaxy and CMB surveys, including the nature of dark energy, modified gravity, and neutrino mass.« less

The special growth history of central galaxies in groups and clusters

NASA Astrophysics Data System (ADS)

Nipoti, Carlo

2017-05-01

Central galaxies (CGs) in galaxy groups and clusters are believed to form and assemble a good portion of their stellar mass at early times, but they also accrete significant mass at late times via galactic cannibalism, that is merging with companion group or cluster galaxies that experience dynamical friction against the common host dark-matter halo. The effect of these mergers on the structure and kinematics of the CG depends not only on the properties of the accreted satellites, but also on the orbital parameters of the encounters. Here we present the results of numerical simulations aimed at estimating the distribution of merging orbital parameters of satellites cannibalized by the CGs in groups and clusters. As a consequence of dynamical friction, the satellites' orbits evolve losing energy and angular momentum, with no clear trend towards orbit circularization. The distributions of the orbital parameters of the central-satellite encounters are markedly different from the distributions found for halo-halo mergers in cosmological simulations. The orbits of satellites accreted by the CGs are on average less bound and less eccentric than those of cosmological halo-halo encounters. We provide fits to the distributions of the central-satellite merging orbital parameters that can be used to study the merger-driven evolution of the scaling relations of CGs.

Particle Dark Matter Searches Outside the Local Group.

PubMed

Regis, Marco; Xia, Jun-Qing; Cuoco, Alessandro; Branchini, Enzo; Fornengo, Nicolao; Viel, Matteo

2015-06-19

If dark matter (DM) is composed by particles which are nongravitationally coupled to ordinary matter, their annihilations or decays in cosmic structures can result in detectable radiation. We show that the most powerful technique to detect a particle DM signal outside the Local Group is to study the angular cross-correlation of nongravitational signals with low-redshift gravitational probes. This method allows us to enhance the signal to noise from the regions of the Universe where the DM-induced emission is preferentially generated. We demonstrate the power of this approach by focusing on GeV-TeV DM and on the recent cross-correlation analysis between the 2MASS galaxy catalogue and the Fermi-LAT γ-ray maps. We show that this technique is more sensitive than other extragalactic γ-ray probes, such as the energy spectrum and angular autocorrelation of the extragalactic background, and emission from clusters of galaxies. Intriguingly, we find that the measured cross-correlation can be well fitted by a DM component, with a thermal annihilation cross section and mass between 10 and 100 GeV, depending on the small-scale DM properties and γ-ray production mechanism. This solicits further data collection and dedicated analyses.

Particle Dark Matter Searches Outside the Local Group

NASA Astrophysics Data System (ADS)

Regis, Marco; Xia, Jun-Qing; Cuoco, Alessandro; Branchini, Enzo; Fornengo, Nicolao; Viel, Matteo

2015-06-01

If dark matter (DM) is composed by particles which are nongravitationally coupled to ordinary matter, their annihilations or decays in cosmic structures can result in detectable radiation. We show that the most powerful technique to detect a particle DM signal outside the Local Group is to study the angular cross-correlation of nongravitational signals with low-redshift gravitational probes. This method allows us to enhance the signal to noise from the regions of the Universe where the DM-induced emission is preferentially generated. We demonstrate the power of this approach by focusing on GeV-TeV DM and on the recent cross-correlation analysis between the 2MASS galaxy catalogue and the Fermi-LAT γ -ray maps. We show that this technique is more sensitive than other extragalactic γ -ray probes, such as the energy spectrum and angular autocorrelation of the extragalactic background, and emission from clusters of galaxies. Intriguingly, we find that the measured cross-correlation can be well fitted by a DM component, with a thermal annihilation cross section and mass between 10 and 100 GeV, depending on the small-scale DM properties and γ -ray production mechanism. This solicits further data collection and dedicated analyses.

The redshift-space neighborhoods of 36 loose groups of galaxies. 1: The data

NASA Technical Reports Server (NTRS)

Ramella, Massimo; Geller, Margaret J.; Hurchra, John P.; Thorstensen, John R.

1995-01-01

We have selected 36 loose groups of galaxies (RGH89) with at least five members, and with mean redshift average value of CZ is greater than 3200 km/s. These groups all lie within the first two slices of the CfA redshift survey 8(sup h) less than or equal to alpha less than or equal to 17(sup h) and 26.5 deg less than or equal to delta less than or equal to 38.5 deg). For each of these groups, we define the redshift-space neighborhood as a region centered on the group coordinates and delimited by a circle of projected radius R(sub cir) = 1.5/h Mpc on the sky, and by a velocity interval delta (sub cz) = 3000 km/s. Here we give the redshifts of 334 galaxies in these redshift-space neighborhoods. For completeness, we also give the redshifts of the 232 original members. These data include 199 new redshifts. We demonstrate that these samples of fainter galaxies significantly increase the number of members.

Percolation galaxy groups and clusters in the sdss redshift survey: identification, catalogs, and the multiplicity function

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berlind, Andreas A.; Frieman, Joshua A.; Weinberg, David H.

2006-01-01

We identify galaxy groups and clusters in volume-limited samples of the SDSS redshift survey, using a redshift-space friends-of-friends algorithm. We optimize the friends-of-friends linking lengths to recover galaxy systems that occupy the same dark matter halos, using a set of mock catalogs created by populating halos of N-body simulations with galaxies. Extensive tests with these mock catalogs show that no combination of perpendicular and line-of-sight linking lengths is able to yield groups and clusters that simultaneously recover the true halo multiplicity function, projected size distribution, and velocity dispersion. We adopt a linking length combination that yields, for galaxy groups withmore » ten or more members: a group multiplicity function that is unbiased with respect to the true halo multiplicity function; an unbiased median relation between the multiplicities of groups and their associated halos; a spurious group fraction of less than {approx}1%; a halo completeness of more than {approx}97%; the correct projected size distribution as a function of multiplicity; and a velocity dispersion distribution that is {approx}20% too low at all multiplicities. These results hold over a range of mock catalogs that use different input recipes of populating halos with galaxies. We apply our group-finding algorithm to the SDSS data and obtain three group and cluster catalogs for three volume-limited samples that cover 3495.1 square degrees on the sky. We correct for incompleteness caused by fiber collisions and survey edges, and obtain measurements of the group multiplicity function, with errors calculated from realistic mock catalogs. These multiplicity function measurements provide a key constraint on the relation between galaxy populations and dark matter halos.« less

First Characterization of the Neutral ISM in Two Local Volume Dwarf Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bralts-Kelly, Lilly; Bulatek, Alyssa M.; Chinski, Sarah

We present the first H i spectral-line images of the nearby, star-forming dwarf galaxies UGC 11411 and UGC 8245, acquired as part of the “Observing for University Classes” program with the Karl G. Jansky Very Large Array (VLA). These low-resolution images localize the H i gas and reveal the bulk kinematics of each system. Comparing with Hubble Space Telescope ( HST ) broadband and ground-based H α imaging, we find that the ongoing star formation in each galaxy is associated with the highest H i mass surface density regions. UGC 8245 has a much lower current star formation rate thanmore » UGC 11411, which harbors very high surface brightness H α emission in the inner disk and diffuse, lower surface brightness nebular gas that extends well beyond the stellar disk as traced by HST . We measure the dynamical masses of each galaxy and find that the halo of UGC 11411 is more than an order of magnitude more massive than the halo of UGC 8245, even though the H i and stellar masses of the sources are similar. We show that UGC 8245 shares similar physical properties with other well-studied low-mass galaxies, while UGC 11411 is more highly dark matter dominated. Both systems have negative peculiar velocities that are associated with a coherent flow of nearby galaxies at high supergalactic latitude.« less

A catalogue of faint local radio AGN and the properties of their host galaxies

NASA Astrophysics Data System (ADS)

Lofthouse, E. K.; Kaviraj, S.; Smith, D. JB; Hardcastle, M. J.

2018-05-01

We present a catalogue of local (z < 0.1) galaxies that contain faint AGN. We select these objects by identifying galaxies that exhibit a significant excess in their radio luminosities, compared to what is expected from the observed levels of star-formation activity in these systems. This is achieved by comparing the optical (spectroscopic) star formation rate (SFR) to the 1.4 GHz luminosity measured from the FIRST survey. The majority of the AGN identified in this study are fainter than those in previous work, such as in the Best and Heckman (2012) catalogue. We show that these faint AGN make a non-negligible contribution to the radio luminosity function at low luminosities (below 1022.5 W Hz-1), and host ˜13 per cent of the local radio luminosity budget. Their host galaxies are predominantly high stellar-mass systems (with a median stellar mass of 1011M⊙), are found across a range of environments (but typically in denser environments than star-forming galaxies) and have early-type morphologies. This study demonstrates a general technique to identify AGN in galaxy populations where reliable optical SFRs can be extracted using spectro-photometry and where radio data are also available so that a radio excess can be measured. Our results also demonstrate that it is unsafe to infer SFRs from radio emission alone, even if bright AGN have been excluded from a sample, since there is a significant population of faint radio AGN which may contaminate the radio-derived SFRs.

H II regions in the dwarf galaxy UGC-A 86

NASA Technical Reports Server (NTRS)

Miller, Bryan W.; Hodge, Paul

1993-01-01

The uncertain nature of the dwarf irregular galaxy UGC-A 86 (VIIZw009) makes it a very interesting object for studying star formation at the low end of the galaxy luminosity function. Saha and Hoessel (1991) find that this object is composed of two main parts, one of which appears more resolved than the other. The more resolved component has an excess of blue stars, suggesting that it is currently undergoing star formation. Thus, they argue that UGC-A 86 could be either a superposition of unrelated galaxies, two interacting galaxies, or a single galaxy. However, surface photometry performed by Richter et al. (1991) indicates that it is a single galaxy with an exponential luminosity profile. Richter et al. also find UGC-A 86 to be extremely dusty and to be associated with the infrared source IRAS 3550+6657. The uncertainty is compounded by the large ambiguity in the distance, though a heliocentric H1 velocity of 80 plus or minus 7 km s(sup -1) suggests that it is either a member of the Local Group or perhaps the IC 342 group. A distance of 1.5 Mpc and a reddening of E(B - V) = 0.65 is adopted. UGC-A 86 in H-alpha was observed in order to measure its current star formation rate. This is part of a larger project to study the star formation rates and histories of a complete sample of dwarf galaxies in the Local Group and other nearby groups. The H region luminosity function and size distribution for UGC-A 86 are presented and compared with previous observations of similar dwarf galaxies.

X-ray analysis of the galaxy group UGC 03957 beyond R200 with Suzaku

NASA Astrophysics Data System (ADS)

Thölken, Sophia; Lovisari, Lorenzo; Reiprich, Thomas H.; Hasenbusch, Jan

2016-07-01

Context. In the last few years, the outskirts of galaxy clusters have been studied in detail and the analyses have brought up interesting results such as indications of possible gas clumping and the breakdown of hydrostatic, thermal, and ionization equilibrium. These phenomena affect the entropy profiles of clusters, which often show deviations from the self-similar prediction around R200. However, significant uncertainties remain for groups of galaxies. In particular the question, of whether entropy profiles are similar to those of galaxy clusters. Aims: We investigated the gas properties of the galaxy group UGC 03957 up to 1.4 R200 ≈ 1.4 Mpc in four azimuthal directions with the Suzaku satellite. We checked for azimuthal symmetry and obtained temperature, entropy, density, and gas mass profiles. Previous studies point to deviations from equilibrium states at the outskirts of groups and clusters and so we studied the hydrodynamical status of the gas at these large radii. Methods: We performed a spectral analysis of five Suzaku observations of UGC 03957 with ~138 ks good exposure time in total and five Chandra snapshot observations for point source detection. We investigated systematic effects such as point spread function and uncertainties in the different background components, and performed a deprojection of the density and temperature profile. Results: We found a temperature drop of a factor of ~3 from the center to the outskirts that is consistent with previous results for galaxy clusters. The metal abundance profile shows a flat behavior towards large radii, which is a hint for galactic winds as the primary ICM enrichment process. The entropy profile is consistent with numerical simulations after applying a gas mass fraction correction. Feedback processes and AGN activity might be one explanation for entropy modification, imprinting out to larger radii in galaxy groups than in galaxy clusters. Previous analyses for clusters and groups often showed an

Multi-wavelength observations of barred, flocculent galaxies

NASA Astrophysics Data System (ADS)

Ratay, Douglas Lee

Although it is generally accepted that large galaxies form through the assemblage of smaller objects, an explanation for the morphology of galaxies is not available. Any complete theory of galaxy morphology must include production and dissolution mechanisms for galactic bars, rings, nuclear bars, spiral arms, and companions. This theory does not exist because of the lack of detailed data from many types of galaxies in different environments. We have defined a new sample of galaxies which are simultaneously flocculent, barred, and isolated. We have performed optical, near-infrared, and radio (HI) observations of the galaxies in this sample. We measured properties of our galaxies including bar length, bar axis ratio, HI diameter, HI mass, and dynamical mass. We found that our sample group is heterogeneous, and compares well to a standard samples of galaxies. We found two of our galaxies to possess companions, and two others to show evidence of current interactions. This is consistent with other observations indicating that local isolated galaxies do not possess a large number of small companions. We cannot rule out the possibility of very small companions. We find that as a group our sample is slightly less luminous than normal galaxies and may be more likely to be involved in interactions. We conclude that the bar and spiral arm features in our sample are due to processes internal to the galaxies, likely involving the interaction between the galactic disk and halo. We defined a control sample of barred, grand design galaxies to further determine the acceptability of barred, flocculent galaxies as a physically meaningful subset of galaxies.

Quenching and ram pressure stripping of simulated Milky Way satellite galaxies

NASA Astrophysics Data System (ADS)

Simpson, Christine; Grand, Robert; Gomez, Facundo; Marinacci, Federico; Pakmor, Rüdiger; Springel, Volker; Campbell, David; Frenk, Carlos; Auriga Project, Virgo Consortium

2018-01-01

We present predictions for the quenching of star formation in satellite galaxies of the Local Group from a suite of 30 cosmological zoom simulations of Milky Way-like host galaxies. The Auriga simulations resolve satellites down to the luminosity of the classical dwarf spheroidal galaxies of the Milky Way. We find strong mass-dependent and distance-dependent quenching signals, where dwarf systems beyond 600 kpc are only strongly quenched below a stellar mass of 107 M⊙. Ram pressure stripping appears to be the dominant quenching mechanism and 50% of quenched systems cease star formation within 1 Gyr of first infall. We demonstrate that systems within a host galaxy's R200 radius are comprised of two populations: (i) a first infall population that has entered the host halo within the past few Gyrs and (ii) a population of returning `backsplash' systems that have had a much more extended interaction with the host. Backsplash galaxies that do not return to the host galaxy by redshift zero exhibit quenching properties similar to galaxies within R200 and are distinct from other external systems. The simulated quenching trend with stellar mass has some tension with observations, but our simulations are able reproduce the range of quenching times measured from resolved stellar populations of Local Group dwarf galaxies.

Quenching and ram pressure stripping of simulated Milky Way satellite galaxies

NASA Astrophysics Data System (ADS)

Simpson, Christine M.; Grand, Robert J. J.; Gómez, Facundo A.; Marinacci, Federico; Pakmor, Rüdiger; Springel, Volker; Campbell, David J. R.; Frenk, Carlos S.

2018-07-01

We present predictions for the quenching of star formation in satellite galaxies of the Local Group from a suite of 30 cosmological zoom simulations of Milky Way-like host galaxies. The Auriga simulations resolve satellites down to the luminosity of the classical dwarf spheroidal galaxies of the Milky Way. We find strong mass-dependent and distance-dependent quenching signals, where dwarf systems beyond 600 kpc are only strongly quenched below a stellar mass of 107 M⊙. Ram pressure stripping appears to be the dominant quenching mechanism and 50 per cent of quenched systems cease star formation within 1 Gyr of first infall. We demonstrate that systems within a host galaxy's R200 radius are comprised of two populations: (i) a first infall population that has entered the host halo within the past few Gyrs and (ii) a population of returning `backsplash' systems that have had a much more extended interaction with the host. Backsplash galaxies that do not return to the host galaxy by redshift zero exhibit quenching properties similar to galaxies within R200 and are distinct from other external systems. The simulated quenching trend with stellar mass has some tension with observations, but our simulations are able reproduce the range of quenching times measured from resolved stellar populations of Local Group dwarf galaxies.

Quenching and ram pressure stripping of simulated Milky Way satellite galaxies

NASA Astrophysics Data System (ADS)

Simpson, Christine M.; Grand, Robert J. J.; Gómez, Facundo A.; Marinacci, Federico; Pakmor, Rüdiger; Springel, Volker; Campbell, David J. R.; Frenk, Carlos S.

2018-03-01

We present predictions for the quenching of star formation in satellite galaxies of the Local Group from a suite of 30 cosmological zoom simulations of Milky Way-like host galaxies. The Auriga simulations resolve satellites down to the luminosity of the classical dwarf spheroidal galaxies of the Milky Way. We find strong mass-dependent and distance-dependent quenching signals, where dwarf systems beyond 600 kpc are only strongly quenched below a stellar mass of 107 M⊙. Ram pressure stripping appears to be the dominant quenching mechanism and 50% of quenched systems cease star formation within 1 Gyr of first infall. We demonstrate that systems within a host galaxy's R200 radius are comprised of two populations: (i) a first infall population that has entered the host halo within the past few Gyrs and (ii) a population of returning `backsplash' systems that have had a much more extended interaction with the host. Backsplash galaxies that do not return to the host galaxy by redshift zero exhibit quenching properties similar to galaxies within R200 and are distinct from other external systems. The simulated quenching trend with stellar mass has some tension with observations, but our simulations are able reproduce the range of quenching times measured from resolved stellar populations of Local Group dwarf galaxies.

UGC 8508 - A dwarf galaxy associated with the M 101 group

NASA Technical Reports Server (NTRS)

Mould, J. R.; Schneider, D. P.; Harding, P.; Bothun, G. D.

1986-01-01

Two-color CCD photometry of UGC 8508 has resolved the system into stars. The color-magnitude diagram shows blue and red supergiants, the apparent magnitudes of the brightest stars indicate that UGC 8508 lies within 2 Mpc of the adopted 6 Mpc distance of the M 101 group. The galaxy contains a significant color gradient; star formation is confined to the central 1.5 scale lengths (0.8 kpc). UGC 8508 has a central surface brightness intermediate between bursting and quiescent dwarf irregular galaxies.

Feeding and feedback in radio galaxies of the local universe

NASA Astrophysics Data System (ADS)

Couto, Guilherme dos Santos

2016-10-01

We present integral field spectroscopic data covering the inner kiloparsecs of four radio galaxies of the local Universe (z<0.07), Arp 102B, Pictor A, 3C 33 and 4C +29.30, obtained with the GMOS-IFU instrument of the Gemini telescopes. We use these data to analyze the gas excitation and kinematics via two-dimensional maps. Using the flux distributions of the emission lines, we identify extended emission in ionized gas up to the edges of the observed field, which corresponds to 1.7 kpc x 2.5 kpc for Arp 102B, 2.5 kpc x 3.4 kpc for Pictor A, 4.0 kpc x 5.8 kpc for 3C 33 and 4.3 kpc x 6.2 kpc for 4C +29.30. The extended line emitting gas displays structures resembling rotating disks, spiral arms and bars. Line ratios indicate that both photons from the nuclear source and shocks originated in the interaction of the radio jet with circumnuclear gas are ionizing mechanisms of the gas. Line ratio values are typical of Seyfert galaxies for 3C 33 and 4C +29.30, while intermediate values between Seyferts and LINERs are observed in Arp 102B. Pictor A galaxy, however, shows low values of [NII]/Ha=0.15-0.25, expected for HII regions. We suggest that these values are observed due to the low gas metallicity (12+log(O/H)=8.39). Centroid velocity maps show that the gas kinematics is dominated by rotation only in Arp 102B and 3C 33. Outflows are observed in the galaxies Arp 102B, 3C 33 and 4C +29.30. We obtain mass outflow rates of 0.32-0.49 Msun per year, but the outflow kinetic power is small, ranging 0.04-0.07% of the AGN bolometric luminosity, indicating that the feedback has little impact in the host galaxies evolution. The high masses of ionized gas, ranging from 7.4E7 to 4.6E8 Msun, and the fact that these galaxies are early-type, suggest an external origin of the gas. Indeed, it is observed evidence of interaction with companion galaxies in Arp 102B, Pictor A and 4C +29.30. We suggest that the capture of mass has triggered the nuclear activity in these galaxies, with the high

DISCOVERY OF AN ULTRA-FAINT DWARF GALAXY IN THE INTRACLUSTER FIELD OF THE VIRGO CENTER: A FOSSIL OF THE FIRST GALAXIES?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jang, In Sung; Lee, Myung Gyoon, E-mail: isjang@astro.snu.ac.kr, E-mail: mglee@astro.snu.ac.kr

2014-11-01

Ultra-faint dwarf galaxies (UFDs) are newcomers among galaxies, and are the faintest galaxies in the observed universe. To date, they have only been found around the Milky Way Galaxy and M31 in the Local Group. We present the discovery of a UFD in the intracluster field in the core of the Virgo cluster (Virgo UFD1), which is far from any massive galaxies. The color-magnitude diagram of the resolved stars in this galaxy shows a narrow red giant branch, similar to those of metal-poor globular clusters in the Milky Way. We estimate its distance by comparing the red giant branch withmore » isochrones, and we obtain a value 16.4 ± 0.4 Mpc. This shows that it is indeed a member of the Virgo cluster. From the color of the red giants we estimate its mean metallicity to be very low, [Fe/H] =–2.4 ± 0.4. Its absolute V-band magnitude and effective radius are derived to be M{sub V} = –6.5 ± 0.2 and r {sub eff} = 81 ± 7 pc, much fainter and smaller than the classical dwarf spheroidal galaxies. Its central surface brightness is estimated to be as low as μ {sub V,} {sub 0} = 26.37 ± 0.05 mag arcsec{sup –2}. Its properties are similar to those of the Local Group analogs. No evidence of tidal features are found in this galaxy. Considering its narrow red giant branch with no asymptotic giant branch stars, low metallicity, and location, it may be a fossil remnant of the first galaxies.« less

Growing massive black holes in a Local Group environment: the central supermassive, slowly sinking and ejected populations

NASA Astrophysics Data System (ADS)

Micic, Miroslav; Holley-Bockelmann, Kelly; Sigurdsson, Steinn

2011-06-01

We explore the growth of ≤107 M⊙ black holes that reside at the centres of spiral and field dwarf galaxies in a Local Group type of environment. We use merger trees from a cosmological N-body simulation known as Via Lactea 2 (VL-2) as a framework to test two merger-driven semi-analytic recipes for black hole growth that include dynamical friction, tidal stripping and gravitational wave recoil in over 20 000 merger tree realizations. First, we apply a Fundamental Plane limited (FPL) model to the growth of Sgr A*, which drives the central black hole to a maximum mass limited by the black hole Fundamental Plane after every merger. Next, we present a new model that allows for low-level prolonged gas accretion (PGA) during the merger. We find that both models can generate an Sgr A* mass black hole. We predict a population of massive black holes in local field dwarf galaxies - if the VL-2 simulation is representative of the growth of the Local Group, we predict up to 35 massive black holes (≤106 M⊙) in Local Group field dwarfs. We also predict that hundreds of ≤105 M⊙ black holes fail to merge, and instead populate the Milky Way halo, with the most massive of them at roughly the virial radius. In addition, we find that there may be hundreds of massive black holes ejected from their hosts into the nearby intergalactic medium due to gravitational wave recoil. We discuss how the black hole population in the Local Group field dwarfs may help to constrain the growth mechanism for Sgr A*.

Galaxy and Mass Assembly (GAMA): Variation in Galaxy Structure Across the Green Valley

NASA Astrophysics Data System (ADS)

Kelvin, Lee S.; Bremer, Malcolm N.; Phillipps, Steven; James, Philip A.; Davies, Luke J. M.; De Propris, Roberto; Moffett, Amanda J.; Percival, Susan M.; Baldry, Ivan K.; Collins, Chris A.; Alpaslan, Mehmet; Bland-Hawthorn, Joss; Brough, Sarah; Cluver, Michelle; Driver, Simon P.; Hashemizadeh, Abdolhosein; Holwerda, Benne W.; Laine, Jarkko; Lara-Lopez, Maritza A.; Liske, Jochen; Maciejewski, Witold; Napolitano, Nicola R.; Penny, Samantha J.; Popescu, Cristina C.; Sansom, Anne E.; Sutherland, Will; Taylor, Edward N.; van Kampen, Eelco; Wang, Lingyu

2018-04-01

Using a sample of 472 local Universe (z < 0.06) galaxies in the stellar mass range 10.25< log M_{\\star }/M_{⊙}<10.75, we explore the variation in galaxy structure as a function of morphology and galaxy colour. Our sample of galaxies is sub-divided into red, green and blue colour groups and into elliptical and non-elliptical (disk-type) morphologies. Using KiDS and VIKING derived postage stamp images, a group of eight volunteers visually classified bars, rings, morphological lenses, tidal streams, shells and signs of merger activity for all systems. We find a significant surplus of rings (2.3σ) and lenses (2.9σ) in disk-type galaxies as they transition across the green valley. Combined, this implies a joint ring/lens green valley surplus significance of 3.3σ relative to equivalent disk-types within either the blue cloud or the red sequence. We recover a bar fraction of ˜44% which remains flat with colour, however, we find that the presence of a bar acts to modulate the incidence of rings and (to a lesser extent) lenses, with rings in barred disk-type galaxies more common by ˜20 - 30 percentage points relative to their unbarred counterparts, regardless of colour. Additionally, green valley disk-type galaxies with a bar exhibit a significant 3.0σ surplus of lenses relative to their blue/red analogues. The existence of such structures rules out violent transformative events as the primary end-of-life evolutionary mechanism, with a more passive scenario the favoured candidate for the majority of galaxies rapidly transitioning across the green valley.

The EDGE-CALIFA Survey: Variations in the Molecular Gas Depletion Time in Local Galaxies

NASA Astrophysics Data System (ADS)

Utomo, Dyas; Bolatto, Alberto D.; Wong, Tony; Ostriker, Eve C.; Blitz, Leo; Sanchez, Sebastian F.; Colombo, Dario; Leroy, Adam K.; Cao, Yixian; Dannerbauer, Helmut; Garcia-Benito, Ruben; Husemann, Bernd; Kalinova, Veselina; Levy, Rebecca C.; Mast, Damian; Rosolowsky, Erik; Vogel, Stuart N.

2017-11-01

We present results from the EDGE survey, a spatially resolved CO(1-0) follow-up to CALIFA, an optical Integral Field Unit survey of local galaxies. By combining the data products of EDGE and CALIFA, we study the variation in molecular gas depletion time (τ dep) on kiloparsec scales in 52 galaxies. We divide each galaxy into two parts: the center, defined as the region within 0.1 {R}25, and the disk, defined as the region between 0.1 and 0.7 {R}25. We find that 14 galaxies show a shorter τ dep (˜1 Gyr) in the center relative to that in the disk (τ dep ˜ 2.4 Gyr), which means the central region in those galaxies is more efficient at forming stars per unit molecular gas mass. This finding implies that the centers with shorter τ dep resemble the intermediate regime between galactic disks and starburst galaxies. Furthermore, the central drop in τ dep is correlated with a central increase in the stellar surface density, suggesting that a shorter τ dep is associated with molecular gas compression by the stellar gravitational potential. We argue that varying the CO-to-H2 conversion factor only exaggerates the central drop of τ dep.

Galaxy evolution in groups and clusters: star formation rates, red sequence fractions and the persistent bimodality

NASA Astrophysics Data System (ADS)

Wetzel, Andrew R.; Tinker, Jeremy L.; Conroy, Charlie

2012-07-01

Using galaxy group/cluster catalogues created from the Sloan Digital Sky Survey Data Release 7, we examine in detail the specific star formation rate (SSFR) distribution of satellite galaxies and its dependence on stellar mass, host halo mass and halo-centric radius. All galaxies, regardless of central satellite designation, exhibit a similar bimodal SSFR distribution, with a strong break at SSFR ≈ 10-11 yr-1 and the same high SSFR peak; in no regime is there ever an excess of galaxies in the 'green valley'. Satellite galaxies are simply more likely to lie on the quenched ('red sequence') side of the SSFR distribution. Furthermore, the satellite quenched fraction excess above the field galaxy value is nearly independent of galaxy stellar mass. An enhanced quenched fraction for satellites persists in groups with halo masses down to 3 × 1011 M⊙ and increases strongly with halo mass and towards halo centre. We find no detectable quenching enhancement for galaxies beyond ˜2 Rvir around massive clusters once these galaxies have been decomposed into centrals and satellites. These trends imply that (1) galaxies experience no significant environmental effects until they cross within ˜Rvir of a more massive host halo; (2) after this, star formation in active satellites continues to evolve in the same manner as active central galaxies for several Gyr; and (3) once begun, satellite star formation quenching occurs rapidly. These results place strong constraints on satellite-specific quenching mechanisms, as we will discuss further in companion papers.

Galaxy and Mass Assembly (GAMA): variation in galaxy structure across the green valley

NASA Astrophysics Data System (ADS)

Kelvin, Lee S.; Bremer, Malcolm N.; Phillipps, Steven; James, Philip A.; Davies, Luke J. M.; De Propris, Roberto; Moffett, Amanda J.; Percival, Susan M.; Baldry, Ivan K.; Collins, Chris A.; Alpaslan, Mehmet; Bland-Hawthorn, Joss; Brough, Sarah; Cluver, Michelle; Driver, Simon P.; Hashemizadeh, Abdolhosein; Holwerda, Benne W.; Laine, Jarkko; Lara-Lopez, Maritza A.; Liske, Jochen; Maciejewski, Witold; Napolitano, Nicola R.; Penny, Samantha J.; Popescu, Cristina C.; Sansom, Anne E.; Sutherland, Will; Taylor, Edward N.; van Kampen, Eelco; Wang, Lingyu

2018-07-01

Using a sample of 472 local Universe (z < 0.06) galaxies in the stellar mass range 10.25 {<} log {M}_{\\star }/{M}_{⊙} {<} 10.75, we explore the variation in galaxy structure as a function of morphology and galaxy colour. Our sample of galaxies is subdivided into red, green, and blue colour groups and into elliptical and non-elliptical (disk-type) morphologies. Using Kilo-Degree Survey (KiDS) and Visible and Infrared Survey Telescope for Astronomy (VISTA) Kilo-Degree Infrared Galaxy Survey (VIKING) derived postage stamp images, a group of eight volunteers visually classified bars, rings, morphological lenses, tidal streams, shells, and signs of merger activity for all systems. We find a significant surplus of rings (2.3σ) and lenses (2.9σ) in disk-type galaxies as they transition across the green valley. Combined, this implies a joint ring/lens green valley surplus significance of 3.3σ relative to equivalent disk-types within either the blue cloud or the red sequence. We recover a bar fraction of {˜ }44 per cent which remains flat with colour, however, we find that the presence of a bar acts to modulate the incidence of rings and (to a lesser extent) lenses, with rings in barred disk-type galaxies more common by ˜20-30 percentage points relative to their unbarred counterparts, regardless of colour. Additionally, green valley disk-type galaxies with a bar exhibit a significant 3.0σ surplus of lenses relative to their blue/red analogues. The existence of such structures rules out violent transformative events as the primary end-of-life evolutionary mechanism, with a more passive scenario the favoured candidate for the majority of galaxies rapidly transitioning across the green valley.

Environmental impacts on dust temperature of star-forming galaxies in the local Universe

NASA Astrophysics Data System (ADS)

Matsuki, Yasuhiro; Koyama, Yusei; Nakagawa, Takao; Takita, Satoshi

2017-04-01

We present infrared views of the environmental effects on the dust properties in star-forming (SF) galaxies at z ˜ 0, using the AKARI Far-Infrared Surveyor all-sky map and the large spectroscopic galaxy sample from Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). We restrict the sample to those within the redshift range of 0.05 < z < 0.07 and the stellar mass range of 9.2 < log 10(M*/M⊙). We select SF galaxies based on their Hα equivalent width (EWHα > 4 Å) and emission line flux ratios. We perform far-infrared (FIR) stacking analyses by splitting the SDSS SF galaxy sample according to their stellar mass, specific star formation rate (SSFRSDSS), and environment. We derive total infrared luminosity (LIR) for each subsample using the average flux densities at WIDE-S (90 μm) and WIDE-L (140 μm) bands, and then compute infrared (IR)-based SFR (SFRIR) from LIR. We find a mild decrease of IR-based SSFR (SSFRIR) amongst SF galaxies with increasing local density (˜0.1-dex level at maximum), which suggests that environmental effects do not instantly shut down the SF activity in galaxies. We also derive average dust temperature (Tdust) using the flux densities at 90 and 140 μm bands. We confirm a strong positive correlation between Tdust and SSFRIR, consistent with recent studies. The most important finding of this study is that we find a marginal trend that Tdust increases with increasing environmental galaxy density. Although the environmental trend is much milder than the SSFR-Tdust correlation, our results suggest that the environmental density may affect the dust temperature in SF galaxies, and that the physical mechanism which is responsible for this phenomenon is not necessarily specific to cluster environments because the environmental dependence of Tdust holds down to relatively low-density environments.

A study of the compact group of galaxies Shahbazian 4

NASA Technical Reports Server (NTRS)

Lynds, C. R.; Khachikian, E. YE.; Amirkhanian, A. S.

1990-01-01

The radial velocities of members of Shakhbazian 4 are determined. It is found that the dispersion of the radial velocities is 440 km/s. The apparent and absolute magnitudes of galaxies in V color are obtained. It is found that the M/L ratio of the group is about 220 solar mass/solar luminosity. The crossing time for the Shakhbazian 4 group is equal to 47 Myr.

Gravitational detection of a low-mass dark satellite galaxy at cosmological distance.

PubMed

Vegetti, S; Lagattuta, D J; McKean, J P; Auger, M W; Fassnacht, C D; Koopmans, L V E

2012-01-18

The mass function of dwarf satellite galaxies that are observed around Local Group galaxies differs substantially from simulations based on cold dark matter: the simulations predict many more dwarf galaxies than are seen. The Local Group, however, may be anomalous in this regard. A massive dark satellite in an early-type lens galaxy at a redshift of 0.222 was recently found using a method based on gravitational lensing, suggesting that the mass fraction contained in substructure could be higher than is predicted from simulations. The lack of very low-mass detections, however, prohibited any constraint on their mass function. Here we report the presence of a (1.9 ± 0.1) × 10(8) M dark satellite galaxy in the Einstein ring system JVAS B1938+666 (ref. 11) at a redshift of 0.881, where M denotes the solar mass. This satellite galaxy has a mass similar to that of the Sagittarius galaxy, which is a satellite of the Milky Way. We determine the logarithmic slope of the mass function for substructure beyond the local Universe to be 1.1(+0.6)(-0.4), with an average mass fraction of 3.3(+3.6)(-1.8) per cent, by combining data on both of these recently discovered galaxies. Our results are consistent with the predictions from cold dark matter simulations at the 95 per cent confidence level, and therefore agree with the view that galaxies formed hierarchically in a Universe composed of cold dark matter.

SDSS-IV MaNGA: Probing the Kinematic Morphology–Density Relation of Early-type Galaxies with MaNGA

NASA Astrophysics Data System (ADS)

Greene, J. E.; Leauthaud, A.; Emsellem, E.; Goddard, D.; Ge, J.; Andrews, B. H.; Brinkman, J.; Brownstein, J. R.; Greco, J.; Law, D.; Lin, Y.-T.; Masters, K. L.; Merrifield, M.; More, S.; Okabe, N.; Schneider, D. P.; Thomas, D.; Wake, D. A.; Yan, R.; Drory, N.

2017-12-01

The “kinematic” morphology–density relation for early-type galaxies posits that those galaxies with low angular momentum are preferentially found in the highest-density regions of the universe. We use a large sample of galaxy groups with halo masses {10}12.5< {M}{halo}< {10}14.5 {h}-1 {M}ȯ observed with the Mapping Nearby Galaxies at APO (MaNGA) survey to examine whether there is a correlation between local environment and rotational support that is independent of stellar mass. We find no compelling evidence for a relationship between the angular momentum content of early-type galaxies and either local overdensity or radial position within the group at fixed stellar mass.

Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

NASA Astrophysics Data System (ADS)

Wheeler, Coral Rose

2016-06-01

The high dark matter content and the shallow potential wells of low mass galaxies (10^3 Msun < Mstar < 10^9.5 Msun) make them excellent testbeds for differing theories of galaxy formation. Additionally, the recent up-tick in the number and detail of Local Group dwarf galaxy observations provides a rich dataset for comparison to simulations that attempt to answer important questions in near field cosmology: why are there so few observed dwarfs compared to the number predicted by simulations? What shuts down star formation in ultra-faint galaxies? Why do dwarfs have inverted age gradients and what does it take to convert a dwarf irregular (dIrrs) into a dwarf spheroidal (dSph) galaxy?We to attempt to answer these questions by running ultra-high resolution cosmological FIRE simulations of isolated dwarf galaxies. We predict that many ultra-faint dwarfs should exist as satellites of more massive isolated Local Group dwarfs. The ultra-faints (Mstar < 10^4 Msun) formed in these simulations have uniformly ancient stellar populations (> 10 Gyr), having had their star formation shut down by reionization. Additionally, we show that the kinematics and ellipticities of isolated simulated dwarf centrals are consistent with observed dSphs satellites without the need for harassment from a massive host. We further show that most (but not all) observed *isolated* dIrrs in the Local Volume also have dispersion-supported stellar populations, contradicting the previous view that these objects are rotating. Finally, we investigate the stellar age gradients in dwarfs — showing that early mergers and strong feedback can create an inverted gradient, with the older stars occupying larger galactocentric radii.These results offer an interesting direction in testing models that attempt to solve dark matter problems via explosive feedback episodes. Can the same models that create large cores in simulated dwarfs preserve the mild stellar rotation that is seen in a minority of isolated d

The Elusive Old Population of the Dwarf Spheroidal Galaxy Leo I.

PubMed

Held; Saviane; Momany; Carraro

2000-02-20

We report the discovery of a significant old population in the dwarf spheroidal (dSph) galaxy Leo I as a result of a wide-area search with the ESO New Technology Telescope. Studies of the stellar content of Local Group dwarf galaxies have shown the presence of an old stellar population in almost all of the dwarf spheroidal galaxies. The only exception was Leo I, which alone appeared to have delayed its initial star formation episode until just a few gigayears ago. The color-magnitude diagram of Leo I now reveals an extended horizontal branch, unambiguously indicating the presence of an old, metal-poor population in the outer regions of this galaxy. Yet we find little evidence for a stellar population gradient, at least outside R>2' (0.16 kpc), since the old horizontal branch stars of Leo I are radially distributed as their more numerous intermediate-age helium-burning counterparts. The discovery of a definitely old population in the predominantly young dwarf spheroidal galaxy Leo I points to a sharply defined first epoch of star formation common to all of the Local Group dSph galaxies as well as to the halo of the Milky Way.

Development of a hot intergalactic medium in spiral-rich galaxy groups: the example of HCG 16

NASA Astrophysics Data System (ADS)

Vrtilek, Jan M.; O'Sullivan, Ewan; David, Laurence P.; Giacintucci, Simona; Zezas, Andreas; Mamon, Gary; Ponman, Trevor J; Raychaudhury, Somak

2014-08-01

Galaxy groups provide the environment in which the majority of galaxies evolve, with low velocity dispersions and small galaxy separations that are conducive to tidal interactions and mergers between group members. X-ray observations reveal the frequent presence of hot gas in groups, with larger quantities linked to early-type galaxies, whereas cold gas is common in spiral-dominated groups. Clarification of the origin and role of the hot medium is central to the understanding of the evolution of the galaxy population and of all phases of the IGM.We here report on the nuclear activity, star formation and the high luminosity X-ray binary populations of the spiral-dominated, likely not yet virialized, group HCG 16, as well as on its intra-group medium, based principally on deep (150 ks) Chandra X-ray observations of the group, as well as new Giant Metrewave Radio Telescope (GMRT) 610 MHz radio data. We confirm the presence of obscured active nuclei in NGC 833 and NGC 835, and identify what may be a previously unrecognized nuclear source in NGC 838; all are variable. NGC 838 and NGC 839 are both starburst-dominated systems, with galactic superwinds that show X-ray and radio evidence of IGM interaction, but only weak nuclear activity; NGC 848 is also dominated by emission from its starburst.We confirm the existence of a faint, extended low-temperature (0.3 keV) intra-group medium, a subject of some uncertainty in earlier studies. The diffuse emission is strongest in a ridge linking the four principal galaxies, and is at least partly coincident with a large-scale HI tidal filament, indicating that the IGM in the inner part of the group is highly multi-phase. We conclude that starburst winds and shock-heating of stripped HI may play an important role in the early stages of IGM formation, with galactic winds contributing 20-40% of the observed hot gas in the system.

The role of submillimetre galaxies in galaxy evolution

NASA Astrophysics Data System (ADS)

Pope, Erin Alexandra

2007-08-01

This thesis presents a comprehensive study of high redshift submillimetre galaxies (SMGs) using the deepest multi-wavelength observations. The submm sample consists of galaxies detected at 850 mm with the Submillimetre Common User Bolometer Array (SCUBA) in the Great Observatories Origins Deep Survey- North region. Using the deep Spitzer Space Telescope images and new data and reductions of the Very Large Array radio data, I find statistically secure counterparts for 60% of the submm sample, and identify tentative counterparts for most of the remaining objects. This is the largest sample of submm galaxies with statistically secure counterparts detected in the radio and with Spitzer . This thesis presents spectral energy distributions (SEDs), Spitzer colours, and infrared (IR) luminosities for the SMGs. A composite rest-frame SED shows that the submm sources peak at longer wavelengths than those of local ultraluminous IR galaxies (ULIRGs), i.e. they appear to be cooler than local ULIRGs of the same luminosity. This demonstrates the strong selection effects, both locally and at high redshift, which may lead to an incomplete census of the ULIRG population. The SEDs of submm galaxies are also different from those of their high redshift neighbours, the near-IR selected BzK galaxies, whose mid-IR to radio SEDs are more like those of local ULIRGs. I fit templates that span the mid-IR through radio to derive the integrated 1R luminosities of the submm galaxies and find a median value of L IR (8-1000 mm) = 6.0 x 10 12 [Special characters omitted.] . I also find that submm flux densities by themselves systematically overpredict L IR when using templates which obey the local ULIRG temperature-luminosity relation. The SED fits show that SMGs are consistent with the correlation between radio and IR luminosity observed in local galaxies. Because the shorter Spitzer wavelengths sample the stellar bump at the redshifts of the submm sources, one can obtain a model independent

Star Formation Suppression in Compact Group Galaxies: A New Path to Quenching?

NASA Astrophysics Data System (ADS)

Alatalo, K.; Appleton, P. N.; Lisenfeld, U.; Bitsakis, T.; Lanz, L.; Lacy, M.; Charmandaris, V.; Cluver, M.; Dopita, M. A.; Guillard, P.; Jarrett, T.; Kewley, L. J.; Nyland, K.; Ogle, P. M.; Rasmussen, J.; Rich, J. A.; Verdes-Montenegro, L.; Xu, C. K.; Yun, M.

2015-10-01

We present CO(1-0) maps of 12 warm H2-selected Hickson Compact Groups (HCGs), covering 14 individually imaged warm H2 bright galaxies, with the Combined Array for Research in Millimeter Astronomy. We found a variety of molecular gas distributions within the HCGs, including regularly rotating disks, bars, rings, tidal tails, and possibly nuclear outflows, though the molecular gas morphologies are more consistent with spirals and early-type galaxies than mergers and interacting systems. Our CO-imaged HCG galaxies, when plotted on the Kennicutt-Schmidt relation, shows star formation (SF) suppression of < {S} > =10+/- 5, distributed bimodally, with five objects exhibiting suppressions of {S} ≳ 10 and depletion timescales ≳10 Gyr. This SF inefficiency is also seen in the efficiency per freefall time of Krumholz et al. We investigate the gas-to-dust ratios of these galaxies to determine if an incorrect LCO-M(H2) conversion caused the apparent suppression and find that HCGs have normal gas-to-dust ratios. It is likely that the cause of the apparent suppression in these objects is associated with shocks injecting turbulence into the molecular gas, supported by the fact that the required turbulent injection luminosity is consistent with the bright H2 luminosity reported by Cluver et al. Galaxies with high SF suppression ({S} ≳ 10) also appear to be those in the most advanced stages of transition across both optical and infrared color space. This supports the idea that at least some galaxies in HCGs are transitioning objects, where a disruption of the existing molecular gas in the system suppresses SF by inhibiting the molecular gas from collapsing and forming stars efficiently. These observations, combined with recent work on poststarburst galaxies with molecular reservoirs, indicates that galaxies do not need to expel their molecular reservoirs prior to quenching SF and transitioning from blue spirals to red early-type galaxies. This may imply that SF quenching can

Hα3: an Hα imaging survey of HI selected galaxies from ALFALFA. IV. Structure of galaxies in the Local and Coma superclusters

NASA Astrophysics Data System (ADS)

Fossati, M.; Gavazzi, G.; Savorgnan, G.; Fumagalli, M.; Boselli, A.; Gutiérrez, L.; Hernández Toledo, H.; Giovanelli, R.; Haynes, M. P.

2013-05-01

Context. We present the analysis of the galaxy structural parameters from Hα3, an Hα narrow-band imaging follow-up survey of ~800 galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Local supercluster, including the Virgo cluster, and in the Coma supercluster. Aims: Taking advantage of Hα3, which provides the complete census of the recent star-forming, HI-rich galaxies in the local universe, we aim to investigate the structural parameters of the young (<10 Myr) and the old (>1 Gyr) stellar populations. By comparing the sizes of these stellar components, we investigated the spatial scale on which galaxies are growing at the present cosmological epoch and the role of the environment in quenching the star-formation activity. Methods: We computed the concentration, asymmetry, and clumpiness (CAS) structural parameters for recently born and old stars. To quantify the sizes we computed half-light radii and a new parameter dubbed EW/r based on the half-light radius of the Hα equivalent width map. To highlight the environmental perturbation, we adopt an updated calibration of the HI-deficiency parameter (DefHI) that we use to divide the sample in unperturbed galaxies (DefHI ≤ 0.3) and perturbed galaxies (DefHI > 0.3). Results: The concentration index computed in the r band depends on the stellar mass and on the Hubble type these variables are related because most massive galaxies are bulge dominated therefore highly concentrated. Going toward later spirals and irregulars the concentration index and the mass decrease along with the bulge-to-disk ratio. Blue compact dwarfs (BCDs) are an exception because they have similar mass, but they are more concentrated than dwarf irregulars. The asymmetry and the clumpiness increase along the spiral sequence up to Sc-Sd, but they decrease going in the dwarf regime, where the light distribution is smooth and more symmetric. When measured on Hα images, the CAS parameters show no obvious correlations with

GalaxyTBM: template-based modeling by building a reliable core and refining unreliable local regions.

PubMed

Ko, Junsu; Park, Hahnbeom; Seok, Chaok

2012-08-10

Protein structures can be reliably predicted by template-based modeling (TBM) when experimental structures of homologous proteins are available. However, it is challenging to obtain structures more accurate than the single best templates by either combining information from multiple templates or by modeling regions that vary among templates or are not covered by any templates. We introduce GalaxyTBM, a new TBM method in which the more reliable core region is modeled first from multiple templates and less reliable, variable local regions, such as loops or termini, are then detected and re-modeled by an ab initio method. This TBM method is based on "Seok-server," which was tested in CASP9 and assessed to be amongst the top TBM servers. The accuracy of the initial core modeling is enhanced by focusing on more conserved regions in the multiple-template selection and multiple sequence alignment stages. Additional improvement is achieved by ab initio modeling of up to 3 unreliable local regions in the fixed framework of the core structure. Overall, GalaxyTBM reproduced the performance of Seok-server, with GalaxyTBM and Seok-server resulting in average GDT-TS of 68.1 and 68.4, respectively, when tested on 68 single-domain CASP9 TBM targets. For application to multi-domain proteins, GalaxyTBM must be combined with domain-splitting methods. Application of GalaxyTBM to CASP9 targets demonstrates that accurate protein structure prediction is possible by use of a multiple-template-based approach, and ab initio modeling of variable regions can further enhance the model quality.

Deep spectroscopy of nearby galaxy clusters - IV. The quench of the star formation in galaxies in the infall region of Abell 85

NASA Astrophysics Data System (ADS)

Aguerri, J. A. L.; Agulli, I.; Méndez-Abreu, J.

2018-06-01

Our aim is to understand the role of the environment in the quenching of star formation of galaxies located in the infall cluster region of Abell 85 (A85). This is achieved by studying the post-starburst galaxy population as tracer of recent quenching. By measuring the equivalent width (EW) of the [O II] and Hδ spectral lines, we classify the galaxies into three groups: passive (PAS), emission line (EL), and post-starburst (PSB) galaxies. The PSB galaxy population represents ˜ 4.5 per cent of the full sample. Dwarf galaxies (Mr > -18.0) account for ˜ 70 - 80 per cent of PSBs, which indicates that most of the galaxies undergoing recent quenching are low-mass objects. Independently of the environment, PSB galaxies are disc-like objects with g - r colour between the blue ELs and the red PAS ones. The PSB and EL galaxies in low-density environments show similar luminosities and local galaxy densities. The dynamics and local galaxy density of the PSB population in high-density environments are shared with PAS galaxies. However, PSB galaxies inside A85 are at shorter clustercentric radius than PAS and EL ones. The value of the EW(Hδ) is larger for those PSBs closer to the cluster centre. We propose two different physical mechanisms producing PSB galaxies depending on the environment. In low-density environments, gas-rich minor mergers or accretions could produce the PSB galaxies. For high-density environments like A85, PSBs would be produced by the removal of the gas reservoirs of EL galaxies by ram-pressure stripping when they pass near the cluster centre.

How well does the Friends-of-Friends algorithm recover group properties from galaxy catalogues limited in both distance and luminosity?

NASA Astrophysics Data System (ADS)

Duarte, Manuel; Mamon, Gary A.

2014-05-01

The specific star formation rates of galaxies are influenced both by their mass and by their environment. Moreover, the mass function of groups and clusters serves as a powerful cosmological tool. It is thus important to quantify the accuracy to which group properties are extracted from redshift surveys. We test here the Friends-of-Friends (FoF) grouping algorithm, which depends on two linking lengths (LLs), plane-of-sky and line-of-sight (LOS), normalized to the mean nearest neighbour separation of field galaxies. We argue, on theoretical grounds, that LLs should be b⊥ ≃ 0.11, and b∥ ≈ 1.3 to recover 95 per cent of all galaxies with projected radii within the virial radius r200 and 95 per cent of the galaxies along the LOS. We then predict that 80 to 90 per cent of the galaxies in FoF groups should lie within their parent real-space groups (RSGs), defined within their virial spheres. We test the FoF extraction for 16 × 16 pairs of LLs, using subsamples of galaxies, doubly complete in distance and luminosity, of a flux-limited mock Sloan Digital Sky Survey (SDSS) galaxy catalogue. We find that massive RSGs are more prone to fragmentation, while the fragments typically have low estimated mass, with typically 30 per cent of groups of low and intermediate estimated mass being fragments. Group merging rises drastically with estimated mass. For groups of three or more galaxies, galaxy completeness and reliability are both typically better than 80 per cent (after discarding the fragments). Estimated masses of extracted groups are biased low, by up to a factor 4 at low richness, while the inefficiency of mass estimation improves from 0.85 dex to 0.2 dex when moving from low to high multiplicity groups. The optimal LLs depend on the scientific goal for the group catalogue. We propose b⊥ ≃ 0.07, with b∥ ≃ 1.1 for studies of environmental effects, b∥ ≃ 2.5 for cosmographic studies and b∥ ≃ 5 for followups of individual groups.

Galaxy clustering dependence on the [O II] emission line luminosity in the local Universe

NASA Astrophysics Data System (ADS)