1,063 research outputs found
Study od a Slice at +9 to +15 degrees of Declination: I. The Neutral Hydrogen Content of Galaxies in Loose Groups
We examine the H1 content of spiral galaxies in groups by using a catalog of
loose groups of galaxies identified in a magnitude limited sample m < 15.7
spanning the range 8 h to 18 h in right ascension and +9 to +15 in declination.
The redshift completeness of the galaxy sample is ~95%. No significant effect
of H1 depletion is found, although there may be a hint that the earliest type
spirals are slightly deficient.Comment: 10 pages, Latex, 3 tables, 5 figures, to appear in the Astronomical
Journa
Redshift-Distance Survey of Early-Type Galaxies. IV. Dipoles of the Velocity Field
We use the recently completed redshift-distance survey of nearby early-type
galaxies (ENEAR) to measure the dipole component of the peculiar velocity field
to a depth of cz ~ 6000 km/s. The sample consists of 1145 galaxies brighter
than m_B=14.5 and cz < 7000 km/s, uniformly distributed over the whole sky, and
129 fainter cluster galaxies within the same volume. Most of the Dn-sigma
distances were obtained from new spectroscopic and photometric observations
conducted by this project, ensuring the homogeneity of the data over the whole
sky. These 1274 galaxies are objectively assigned to 696 objects -- 282
groups/clusters and 414 isolated galaxies. We find that within a volume of
radius ~ 6000 km/s, the best-fitting bulk flow has an amplitude of |vbulk| =220
+/- 42 km/s in the CMB restframe, pointing towards l=304 +/- 16 degrees, b=25
+/- 11 degrees. The error in the amplitude includes statistical, sampling and
possible systematic errors. This solution is in excellent agreement with that
obtained by the SFI Tully-Fisher survey. Our results suggest that most of the
motion of the Local Group is due to fluctuations within 6000 km/s, in contrast
to recent claims of large amplitude bulk motions on larger scales.Comment: 11 pages, 2 figures, ApJL, accepted (updated results; matches
accepted version
A Deep Search For Faint Galaxies Associated With Very Low-redshift C IV Absorbers: III. The Mass- and Environment-dependent Circumgalactic Medium
Using Hubble Space Telescope Cosmic Origins Spectrograph observations of 89
QSO sightlines through the Sloan Digital Sky Survey footprint, we study the
relationships between C IV absorption systems and the properties of nearby
galaxies as well as large-scale environment. To maintain sensitivity to very
faint galaxies, we restrict our sample to 0.0015 < z < 0.015, which defines a
complete galaxy survey to L > 0.01 L* or stellar mass log M_* > 8 Msun. We
report two principal findings. First, for galaxies with impact parameter rho <
1 rvir, C IV detection strongly depends on the luminosity/stellar mass of the
nearby galaxy. C IV is preferentially associated with galaxies with log M_* >
9.5 Msun; lower mass galaxies rarely exhibit significant C IV absorption
(covering fraction f = 9 +12-6% for 11 galaxies with log M_* < 9.5 Msun).
Second, C IV detection within the log M_* > 9.5 Msun population depends on
environment. Using a fixed-aperture environmental density metric for galaxies
with rho < 160 kpc at z < 0.055, we find that 57+/-12% (8/14) of galaxies in
low-density regions (regions with fewer than seven L > 0.15 L* galaxies within
1.5 Mpc) have affiliated C IV absorption; however, none (0/7) of the galaxies
in denser regions show C IV. Similarly, the C IV detection rate is lower for
galaxies residing in groups with dark-matter halo masses of log Mhalo > 12.5
Msun. In contrast to C IV, H I is pervasive in the CGM without regard to mass
or environment. These results indicate that C IV absorbers with log N(C IV) >
13.5 cm^-2 trace the halos of log M_* > 9.5 Msun galaxies but also reflect
larger scale environmental conditions.Comment: 26 pages, 13 figures. ApJ, in pres
Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indices for an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984 had no previous measures. This sample contains the largest set of homogeneous spectroscopic data for a uniform sample of elliptical galaxies in the nearby universe. These galaxies were observed as part of the ENEAR project, designed to study the peculiar motions and internal properties of the local early-type galaxies. Using 523 repeated observations of 317 galaxies obtained during different runs, the data are brought to a common zero point. These multiple observations, taken during the many runs and different instrumental setups employed for this project, are used to derive statistical corrections to the data and are found to be relatively small, typically 5% of the velocity dispersion and 0.01 mag in the Mg2 line strength. Typical errors are about 8% in velocity dispersion and 0.01 mag in Mg2, in good agreement with values published elsewhere
AEGIS: The color-magnitude relation for X-ray selected AGN
We discuss the relationship between rest-frame color and optical luminosity
for X-ray sources in the range 0.6<z<1.4 selected from the Chandra survey of
the Extended Groth Strip (EGS). These objects are almost exclusively active
galactic nuclei (AGN). While there are a few luminous QSOs, most are relatively
weak or obscured AGN whose optical colors should be dominated by host galaxy
light. The vast majority of AGN hosts at z~1 are luminous and red, with very
few objects fainter than M_{B}=-20.5 or bluer than U-B=0.6. This places the AGN
in a distinct region of color-magnitude space, on the ``red sequence'' or at
the top of the ``blue cloud'', with many in between these two modes in galaxy
color. A key stage in the evolution of massive galaxies is when star formation
is quenched, resulting in a migration from the blue cloud to the red sequence.
Our results are consistent with scenarios in which AGN either cause or maintain
this quenching. The large numbers of red sequence AGN imply that strong,
ongoing star formation is not a necessary ingredient for AGN activity, as black
hole accretion appears often to persist after star formation has been
terminated.Comment: 5 pages, 2 figures, accepted for publication in AEGIS ApJ Letters
special editio
- …