79 research outputs found
The Dependence of the Galaxy Luminosity Function on Environment
We present luminosity functions for galaxies in loose groups in the Las
Campanas Redshift Survey, differentiated by their environment (defined by the
line-of-sight velocity dispersion sigma of the host groups) and also by their
spectral type (emission or non-emission, defined by the equivalent width of the
3727-Angstrom [OII] line).
We find systematic variations in the Schechter parameters alpha and M* for
non-emission line galaxies over a range of 0 < sigma < 800 km/s. Alpha varies
from 0.20 to -0.91, indicating an increase in the steepness of the faint end
slope with increasing sigma. The accompanying variation in M* appears to be
accounted for by the intrinsic correlation with alpha and does not indicate a
significant physical variation in the bright end of the luminosity function.
For emission line galaxies, we find no significant systematic variation of the
luminosity function with the environment. Our results show that emission and
non-emission galaxies generally occupy two distinct regions in the alpha-M*
parameter space. From our luminosity functions, we derive the number ratios of
emission to non-emission galaxies as a function of environment and absolute
magnitude, showing that the relative abundance of non-emission line galaxies
generally increases for all magnitudes -23 < M_R < -17.5 towards high-sigma
environments, from ~80% to >90% at M_R = -22 and from ~10% to >50% at M_R = -18
(H_0 = 100 km s^{-1} Mpc^{-1} and q_0 = 0.5).Comment: 34 pages, 10 figures; accepted for publication in the Ap
Galaxy Luminosity Functions from Deep Spectroscopic Samples of Rich Clusters
Using a new spectroscopic sample and methods accounting for spectroscopic
sampling fractions that vary in magnitude and surface brightness, we present
R-band galaxy luminosity functions (GLFs) for six nearby galaxy clusters with
redshifts 4000 < cz < 20000 km/s and velocity dispersions 700 < sigma < 1250
km/s. In the case of the nearest cluster, Abell 1060, our sample extends to
M_R=-14 (7 magnitudes below M*), making this the deepest spectroscopic
determination of the cluster GLF to date. Our methods also yield composite GLFs
for cluster and field galaxies to M_R=-17 (M*+4), including the GLFs of
subsamples of star forming and quiescent galaxies. The composite GLFs are
consistent with Schechter functions (M*_R=-21.14^{+0.17}_{-0.17},
alpha=-1.21^{+0.08}_{-0.07} for the clusters, M*_R=-21.15^{+0.16}_{-0.16},
alpha=-1.28^{+0.12}_{-0.11} for the field). All six cluster samples are
individually consistent with the composite GLF down to their respective
absolute magnitude limits, but the GLF of the quiescent population in clusters
is not universal. There are also significant variations in the GLF of quiescent
galaxies between the field and clusters that can be described as a steepening
of the faint end slope. The overall GLF in clusters is consistent with that of
field galaxies, except for the most luminous tip, which is enhanced in clusters
versus the field. The star formation properties of giant galaxies are more
strongly correlated with the environment than those of fainter galaxies.Comment: 53 pages, 8 figures, 1 ASCII table; accepted for publication in Ap
Disentangling Morphology, Star Formation, Stellar Mass, and Environment in Galaxy Evolution
We present a study of the spectroscopic and photometric properties of
galaxies in six nearby clusters. We perform a partial correlation analysis on
our dataset to investigate whether the correlation between star formation rates
in galaxies and their environment is merely another aspect of correlations of
morphology, stellar mass, or mean stellar age with environment, or whether star
formation rates vary independently of these other correlations. We find a
residual correlation of ongoing star formation with environment, indicating
that even galaxies with similar morphologies, stellar masses, and mean stellar
ages have lower star formation rates in denser environments. Thus, the current
star formation gradient in clusters is not just another aspect of the
morphology-density, stellar mass-density, or mean stellar age-density
relations. Furthermore, the star formation gradient cannot be solely the result
of initial conditions, but must partly be due to subsequent evolution through a
mechanism (or mechanisms) sensitive to environment. Our results constitute a
true ``smoking gun'' pointing to the effect of environment on the later
evolution of galaxies.Comment: 31 pages, including 5 figures; accepted for publication in Ap
The Kinematic Properties of the Extended Disks of Spiral Galaxies: A Sample of Edge-On Galaxies
We present a kinematic study of the outer regions (R_25<R<2 R_25) of 17
edge-on disk galaxies. Using deep long-slit spectroscopy (flux sensitivity a
few 10^-19 erg s^-1 cm^-2 arcsec^-2), we search for H-alpha emission, which
must be emitted at these flux levels by any accumulation of hydrogen due to the
presence of the extragalactic UV background and any other, local source of UV
flux. We present results from the individual galaxy spectra and a stacked
composite. We detect H-alpha in many cases well beyond R_25 and sometimes as
far as 2 R_25. The combination of sensitivity, spatial resolution, and
kinematic resolution of this technique thus provides a powerful complement to
21-cm observations. Kinematics in the outer disk are generally disk-like (flat
rotation curves, small velocity dispersions) at all radii, and there is no
evidence for a change in the velocity dispersion with radius. We place strong
limits, few percent, on the existence of counter-rotating gas out to 1.5 R_25.
These results suggest that thin disks extend well beyond R_25; however, we also
find a few puzzling anomalies. In ESO 323-G033 we find two emission regions
that have velocities close to the systemic velocity rather than the expected
rotation velocity. These low relative velocities are unlikely to be simply due
to projection effects and so suggest that these regions are not on disk-plane,
circular orbits. In MCG-01-31-002 we find emission from gas with a large
velocity dispersion that is co-rotating with the inner disk.Comment: 18 pages, 14 figures, accepted for publication in Ap
What Fraction of Gravitational Lens Galaxies Lie in Groups?
We predict how the observed variations in galaxy populations with environment
affect the number and properties of gravitational lenses in different
environments. Two trends dominate: lensing strongly favors early-type galaxies,
which tend to lie in dense environments, but dense environments tend to have a
larger ratio of dwarf to giant galaxies than the field. The two effects nearly
cancel, and the distribution of environments for lens and non-lens galaxies are
not substantially different (lens galaxies are slightly less likely than
non-lens galaxies to lie in groups and clusters). We predict that about 20% of
lens galaxies are in bound groups (defined as systems with a line-of-sight
velocity dispersion sigma in the range 200 < sigma < 500 km/s), and another
roughly 3% are in rich clusters (sigma > 500 km/s). Therefore at least roughly
25% of lenses are likely to have environments that significantly perturb the
lensing potential. If such perturbations do not significantly increase the
image separation, we predict that lenses in groups have a mean image separation
that is about 0.2'' smaller than that for lenses in the field and estimate that
20-40 lenses in groups are required to test this prediction with significance.
The tail of the distribution of image separations is already illuminating.
Although lensing by galactic potential wells should rarely produce lenses with
image separations theta >~ 6'', two such lenses are seen among 49 known lenses,
suggesting that environmental perturbations of the lensing potential can be
significant. Further comparison of theory and data will offer a direct probe of
the dark halos of galaxies and groups and reveal the extent to which they
affect lensing estimates of cosmological parameters.Comment: 32 pages, 6 embedded figures; accepted for publication in Ap
The Environmental Dependence of the Infrared Luminosity and Stellar Mass Functions
We investigate the dependence of the galaxy infrared luminosity function (LF)
and the associated stellar mass function (SMF) on environment and spectral type
using photometry from the Two Micron All Sky Survey and redshifts from the Las
Campanas Redshift Survey for galaxies brighter than M_J<-19+5 log h. In the
field environment, galaxies with emission lines have LFs with much steeper
faint end slopes (alpha_J=-1.39) than galaxies without emission lines
(alpha_J=-0.59). In the cluster environment, however, even the non-emission
line galaxies have a steep faint-end LF (alpha_J=-1.22). There is also a
significant (95%) difference between the overall cluster and field LFs, . All of these variations are more
pronounced in the SMFs, which we compute by relating the strength of the 4000 A
break in the optical spectra to a mass-to-light ratio.Comment: 14 pages, 13 figures, emulateapj style ApJ, post-referee. Very minor
changes, mostly typographical in natur
VPMS J1342+2840 - an unusual quasar from the variability and proper motion survey
We report the discovery of the highly peculiar, radio-loud quasar VPMS
J1342+2840 (z ~ 1.3) from the variability and proper motion survey. We present
spectroscopic, imaging and photometric observations. The unusual spectrum shows
a strong depression of the continuum over a wide wavelength range in the blue
part without the typical structures of broad absorption line (BAL) troughs. The
image of the quasar is unresolved and there is no evidence for a foreground
object on the line of sight. The broad-band spectral energy distribution is not
consistent with obvious dust reddening with the standard SMC extinction curve.
The downturn of the continuum flux of VPMS J1342+2840 at short wavelengths can
be caused by dust reddening only if the reddening curve is steeper then the SMC
curve in the ultraviolet and is very flat at longer wavelengths. Alternatively,
the dominant spectral features can be explained by low-ionization BALs forming
unusually wide, overlapping absorption troughs.Comment: 4 pages, 3 figures, accepted for publication in A&A Letter
Clustering and descendants of MUSYC galaxies at z<1.5
We measure the evolution of galaxy clustering out to a redshift of z~1.5
using data from two MUSYC fields, the Extended Hubble Deep Field South (EHDF-S)
and the Extended Chandra Deep Field South (ECDF-S). We use photometric redshift
information to calculate the projected-angular correlation function,
omega(sigma), from which we infer the projected correlation function Xi(sigma).
We demonstrate that this technique delivers accurate measurements of clustering
even when large redshift measurement errors affect the data. To this aim we use
two mock MUSYC fields extracted from a LambdaCDM simulation populated with
GALFORM semi-analytic galaxies which allow us to assess the degree of accuracy
of our estimates of Xi(sigma) and to identify and correct for systematic
effects in our measurements. We study the evolution of clustering for volume
limited subsamples of galaxies selected using their photometric redshifts and
rest-frame r-band absolute magnitudes. We find that the real-space correlation
length r_0 of bright galaxies, M_r<-21 (rest-frame) can be accurately recovered
out to z~1.5, particularly for ECDF-S given its near-infrared photometric
coverage. There is mild evidence for a luminosity dependent clustering in both
fields at the low redshift samples (up to =0.57), where the correlation
length is higher for brighter galaxies by up to 1Mpc/h between median
rest-frame r-band absolute magnitudes of -18 to -21.5. As a result of the
photometric redshift measurement, each galaxy is assigned a best-fit template;
we restrict to E and E+20%Sbc types to construct subsamples of early type
galaxies (ETGs). Our ETG samples show a strong increase in r_0 as the redshift
increases, making it unlikely (95% level) that ETGs at median redshift
z_med=1.15 are the direct progenitors of ETGs at z_med=0.37 with equivalent
passively evolved luminosities. (ABRIDGED)Comment: 16 pages, 12 figures, 2 tables, accepted for publication in MNRA
Star Formation in the Milky Way and Nearby Galaxies
We review progress over the past decade in observations of large-scale star
formation, with a focus on the interface between extragalactic and Galactic
studies. Methods of measuring gas contents and star formation rates are
discussed, and updated prescriptions for calculating star formation rates are
provided. We review relations between star formation and gas on scales ranging
from entire galaxies to individual molecular clouds.Comment: 55 pages, 15 figures, in press for Annual Reviews of Astronomy and
Astrophysics; Updated with corrected equation 5, improved references, and
other minor change
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