The transformations that take place in late‐type galaxies in the environment of rich clusters of galaxies at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $z=0$ \end{document} are reviewed. From the handful of late‐type galaxies that inhabit local clusters, whether they were formed in situ and survived as such, avoiding transformation or even destruction, or if they are newcomers that have recently fallen in from outside, we can learn an important lesson on the latest stages of galaxy evolution. We start by reviewing t...

https://iopscience.iop.org/article/10.1086/500691/pdf

Environmental Effects on Late-Type Galaxies in Nearby Clusters

We have measured the equivalent width of the Hα emission line for 11 006 galaxies brighter than M_b-=-−19 (Ω_Λ = 0.7, Ω_m = 0.3, H_0 = 70 km s^(−1) Mpc^(−1)) at 0.05 < z < 0.1 in the 2dF Galaxy Redshift Survey (2dFGRS), in the fields of 17 known galaxy clusters. The limited redshift range ensures that our results are insensitive to aperture bias, and to residuals from night sky emission lines. We use these measurements to trace μ*, the star formation rate normalized to L*, as a function of distance from the cluster centre, and local projected galaxy density. We find that the distribution of μ* steadily skews toward larger values with increasing distance from the cluster centre, converging to the field distribution at distances greater than ∼3 times the virial radius. A correlation between star formation rate and local projected density is also found, which is independent of cluster velocity dispersion and disappears at projected densities below ∼1 galaxy Mpc^(−2) (brighter than M_b = −19). This characteristic scale corresponds approximately to the mean density at the cluster virial radius. The same correlation holds for galaxies more than two virial radii from the cluster centre. We conclude that environmental influences on galaxy properties are not restricted to cluster cores, but are effective in all groups where the density exceeds this critical value. The present-day abundance of such systems, and the strong evolution of this abundance, makes it likely that hierarchical growth of structure plays a significant role in decreasing the global average star formation rate. Finally, the low star formation rates well beyond the virialized cluster rule out severe physical processes, such as ram pressure stripping of disc gas, as being completely responsible for the variations in galaxy properties with environment.

/pdf/the-2df-galaxy-redshift-survey-the-environmental-dependence-9m0ukw88vg.pdf

The 2dF Galaxy Redshift Survey: The environmental dependence of galaxy star formation rates near clusters

We present the results of a new VLA H I Imaging survey of Virgo galaxies, the VLA Imaging survey of Virgo galaxies in Atomic gas (VIVA). The survey includes high-resolution H I data of 53 carefully selected late type galaxies (48 spirals and five irregular systems). The goal is to study environmental effects on H I gas properties of cluster galaxies to understand which physical mechanisms affect galaxy evolution in different density regions, and to establish how far out the impact of the cluster reaches. As a dynamically young cluster, Virgo contains examples of galaxies experiencing a variety of environmental effects. Its nearness allows us to study each galaxy in great detail. We have selected Virgo galaxies with a range of star formation properties in low to high density regions (at projected distances from M87, d 87 = 0.3-3.3 Mpc). Contrary to previous studies, more than half of the galaxies in the sample (~60%) are fainter than 12 mag in BT . Overall, the selected galaxies represent the late type Virgo galaxies (S0/a to Sd/Irr) down to mp 14.6 fairly well in morphological type, systemic velocity, subcluster membership, H I mass, and deficiency. The H I observations were done in C short (CS) configuration of the VLA radio telescope, with a typical spatial resolution of 15'' and a column density sensitivity of 3-5 × 1019 cm–2 in 3σ per 10 km s–1 channel. The survey was supplemented with data of comparable quality from the NRAO archive, taken in CS or C configuration. In this paper, we present H I channel maps, total intensity maps, velocity fields, velocity dispersions, global/radial profiles, position-velocity diagrams and overlays of H I/1.4 GHz continuum maps on the optical images. We also present H I properties such as total flux (S H I ), H I mass (M H I ), linewidths (W 20 and W 50), velocity (V H I ), deficiency (def H I ), and size (D eff H I and D iso H I ), and describe the H I morphology and kinematics of individual galaxies in detail. The survey has revealed details of H I features that were never seen before. In this paper, we briefly discuss differences in typical H I morphology for galaxies in regions of different galaxy densities. We confirm that galaxies near the cluster core (d 87 0.5 Mpc) have H I disks that are smaller compared to their stellar disks (D H I /D 25 < 0.5). Most of these galaxies in the core also show gas displaced from the disk, which is either currently being stripped or falling back after a stripping event. At intermediate distances (d 87 ~ 1 Mpc) from the center, we find a remarkable number of galaxies with long one-sided H I tails pointing away from M87. In a previous letter, we argue that these galaxies are recent arrivals, falling into the Virgo core for the first time. In the outskirts, we find many gas-rich galaxies, with gas disks extending far beyond their optical disks. Interestingly, we also find some galaxies with H I disks that are smaller compared to their stellar disks at large clustercentric distances.

Vla imaging of virgo spirals in atomic gas (viva). i. the atlas and the h i properties

We analyse the observed correlation between galaxy environment and Halpha emission-line strength, using volume-limited samples and group catalogues of 24 968 galaxies at 0.05 < z < 0.095, drawn from the 2dF Galaxy Redshift Survey (M-bJ < -19.5) and the Sloan Digital Sky Survey (M-r < -20.6). We characterize the environment by: (1) Sigma(5), the surface number density of galaxies determined by the projected distance to the fifth nearest neighbour; and (2) rho(1.1) and rho(5.5), three-dimensional density estimates obtained by convolving the galaxy distribution with Gaussian kernels of dispersion 1.1 and 5.5 Mpc, respectively. We find that star-forming and quiescent galaxies form two distinct populations, as characterized by their H equivalent width, W-0(Halpha). The relative numbers of star-forming and quiescent galaxies vary strongly and continuously with local density. However, the distribution of W-0(Halpha) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, rho(5.5), which is likely independent of the trend with local density, rho(1.1). We use two differently selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for sigma = 200-1000 km s(-1). Even in the lowest-density environments, no more than similar to70 per cent of galaxies show significant Halpha emission. Based on these results, we conclude that the present-day correlation between star formation rate and environment is a result of short-time-scale mechanisms that take place preferentially at high redshift, such as starbursts induced by galaxy-galaxy interactions.

https://researchbank.swinburne.edu.au/file/1326e4cd-120c-4c0f-8947-aeb005b6f371/1/PDF (Accepted manuscript).pdf

Galaxy ecology: groups and low-density environments in the SDSS and 2dFGRS

We present the HIPASS Bright Galaxy Catalog (BGC), which contains the 1000 H I brightest galaxies in the southern sky as obtained from the H i Parkes All-Sky Survey ( HIPASS). The selection of the brightest sources is based on their H I peak flux density (S-peak greater than or similar to116 mJy) as measured from the spatially integrated HIPASS spectrum. The derived H I masses range from similar to10(7) to 4 x 10(10) M-.. While the BGC ( z 10degrees. Therefore, the BGC yields no evidence for a population of free-floating'' intergalactic H I clouds without associated optical counterparts. HIPASS provides a clear view of the local large-scale structure. The dominant features in the sky distribution of the BGC are the Supergalactic Plane and the Local Void. In addition, one can clearly see the Centaurus Wall, which connects via the Hydra and Antlia Clusters to the Puppis Filament. Some previously hardly noticable galaxy groups stand out quite distinctly in the H I sky distribution. Several new structures, including some not behind the Milky Way, are seen for the first time.

/pdf/the-1000-brightest-hipass-galaxies-h-i-properties-c93dxue76g.pdf

The 1000 Brightest HIPASS Galaxies: H I Properties

We derive the atomic hydrogen content for a total of 1900 spirals in the fields of 18 nearby clusters. By comparing the H I-deficiency distributions of the galaxies inside and outside one Abell radius (RA) of each cluster, we find that two-thirds of the clusters in our sample show a dearth of neutral gas in their interiors. Possible connections between the gaseous deficiency and the characteristics of both the underlying galaxies and their environment are investigated in order to gain insight into the mechanisms responsible for H I depletion. While we do not find a statistically significant variation of the fraction of H I-deficient spirals in a cluster with its global properties, a number of correlations emerge that argue in favor of the interplay between spiral disks and their environment. In the clusters in which neutral gas deficiency is pronounced, we see clear indications that the degree of H I depletion is related to the morphology of the galaxies and not to their optical size; early-type and probably dwarf spirals are more easily emptied of gas than the intermediate Sbc-Sc types. Gas contents below 1/10, and even 1/100, of the expectation value have been measured, implying that gas removal is very efficient. The radial extent of the region with significant gas ablation can reach up to 2RA. Within this zone, the proportion of gas-poor spirals increases continuously toward the cluster center. The wealth of 21 cm data collected for the Virgo region has made it possible to study the two-dimensional pattern of H I deficiency in that cluster. The map of gas deficiency in the Virgo central area points to an scenario in which gas losses result from the interaction of the disks with the inner hot intracluster gas around M87. We also find evidence that gas-poor spirals in H I-deficient clusters move in orbits more radial than those of the gas-rich objects. The implications of all these results on models of how galaxies interact with their environment are reviewed. Hydrodynamic effects appear as the most plausible cause of H I removal.

The H I Content of Spirals. II. Gas Deficiency in Cluster Galaxies

We derive the atomic hydrogen content for a total of 1900 spirals in the fields of eighteen nearby clusters. By comparing the HI deficiency distributions of the galaxies inside of and outside of one Abell radius of each cluster, we find that two thirds of the clusters in our sample show a dearth of neutral gas in their interiors. Possible connections between the gaseous deficiency and the characteristics of both the underlying galaxies and their environment are investigated in order to gain insight into the mechanisms responsible for HI depletion. While we do not find a statistically significant variation of the fraction of HI-deficient spirals in a cluster with its global properties, a number of correlations emerge that argue in favor of the interplay between spiral disks and their environment. In the clusters in which neutral gas deficiency is pronounced, we see clear indications that the degree of HI depletion is related to the morphology of the galaxies and not to their optical size: early-type and, probably, dwarf spirals are more easily emptied of gas than the intermediate Sbc--Sc types. The wealth of 21-cm data collected for the Virgo region has made it possible to study the 2D pattern of HI deficiency in that cluster. We also find evidence that gas-poor spirals in HI-deficient clusters move on orbits more radial than those of the gas-rich objects. The implications of all these results on models of how galaxies interact with their environment are reviewed. Hydrodynamic effects appear as the most plausible cause of HI removal. (abridged)

The HI Content of Spirals. II. Gas Deficiency in Cluster Galaxies

We have developed a computationally competitive N-body model of a previrialized aggregation of galaxies in a flat Lambda cold dark matter Universe to assess the role of the multiple mergers that take place during the formation stage of such systems in the configuration of the remnants assembled at their centres. An analysis of a suite of 48 simulations of low-mass forming groups (M-tot,M- (gr) similar to 10(13) h(-1)M(circle dot)) demonstrates that the gravitational dynamics involved in their hierarchical collapse is capable of creating realistic first-ranked galaxies without the aid of dissipative processes. Our simulations indicate that the brightest group galaxies (BGGs) constitute a distinct population from other group members, sketching a scenario in which the assembly path of these objects is dictated largely by the formation of their host system. We detect significant differences in the distribution of S ` ersic indices and total magnitudes, as well as a luminosity gap between BGGs and the next brightest galaxy that is positively correlated with the total luminosity of the parent group. Such gaps arise from both the grow of BGGs at the expense of lesser companions and the decrease in the relevance of secondranked objects in equal measure. This results in a dearth of intermediate-mass galaxies which explains the characteristic central dip detected in their luminosity functions in dynamically young galaxy aggregations. The fact that the basic global properties of our BGGs define a thin mass Fundamental Plane strikingly similar to that followed by giant early-type galaxies in the local Universe reinforces confidence in the results obtained.

/pdf/forming-first-ranked-early-type-galaxies-through-4wyiefqr2s.pdf

Forming first-ranked early-type galaxies through hierarchical dissipationless merging

We have developed a computationally competitive N-body model of a previrialized aggregation of galaxies in a flat LambdaCDM universe to assess the role of the multiple mergers that take place during the formation stage of such systems in the configuration of the remnants assembled at their centres. An analysis of a suite of 48 simulations of low-mass forming groups (of about 1E13 solar masses) demonstrates that the gravitational dynamics involved in their hierarchical collapse is capable of creating realistic first-ranked galaxies without the aid of dissipative processes. Our simulations indicate that the brightest group galaxies (BGGs) constitute a distinct population from other group members, sketching a scenario in which the assembly path of these objects is dictated largely by the formation of their host system. We detect significant differences in the distribution of Sersic indices and total magnitudes, as well as a luminosity gap between BGGs and the next brightest galaxy that is positively correlated with the total luminosity of the parent group. Such gaps arise from both the grow of BGGs at the expense of lesser companions and the decrease in the relevance of second-ranked objects in equal measure. This results in a dearth of intermediate-mass galaxies which explains the characteristic central dip detected in their luminosity functions in dynamically young galaxy aggregations. The fact that the basic global properties of our BGGs define a thin mass fundamental plane strikingly similar to that followed giant early-type galaxies in the local universe reinforces confidence in the results obtained.

Carlos García-Gómez

Papers

The H I Content of Spirals. II. Gas Deficiency in Cluster Galaxies

The HI Content of Spirals. II. Gas Deficiency in Cluster Galaxies

Forming first-ranked early-type galaxies through hierarchical dissipationless merging

Forming first-ranked early-type galaxies through hierarchical dissipationless merging