108 research outputs found
Revisiting the low-luminosity galaxy population of the NGC 5846 group with SDSS
Low-luminosity galaxies are known to outnumber the bright galaxy population
in poor groups and clusters of galaxies. Yet, the investigation of
low-luminosity galaxy populations outside the Local Group remains rare and the
dependence on different group environments is still poorly understood. Previous
investigations revealed photometric scaling relations for early-type dwarfs and
a strong dependence of morphology with environment.
The present study aims to analyse the photometric and spectroscopic
properties of the low-luminosity galaxy population in the nearby, well-evolved
and early-type dominated NGC 5846 group of galaxies. It is the third most
massive aggregate of early-type galaxies after the Virgo and Fornax clusters in
the local universe. Photometric scaling relations and the distribution of
morphological types as well as the characteristics of emission-line galaxies
are investigated.
Spectroscopically selected low-luminosity group members from the Sloan
Digital Sky Survey with cz<3000 km/s within a radius of 2 deg=0.91 Mpc around
NGC 5846 are analysed. Surface brightness profiles of early-type galaxies are
fit by a Sersic model r^(1/n). Star formation rates, oxygen abundances and
emission characteristics are determined for emission-line galaxies. [abridged]Comment: 13 pages, 10 figures; accepted for publication in A&
The Extraordinary `Superthin' Spiral Galaxy UGC7321. I. Disk Color Gradients and Global Properties from Multiwavelength Observations
We present B- and R-band imaging and photometry, H-alpha narrow-band imaging,
NIR H-band imaging, and HI 21-cm spectroscopy of the nearby Sd spiral galaxy
UGC7321. UGC7321 exhibits a remarkably thin stellar disk with no bulge
component. The galaxy has a very diffuse, low surface brightness disk, which
appears to suffer little internal extinction in spite of its edge-on geometry.
The UGC7321 disk shows significant B-R color gradients in both the radial and
vertical directions. These color gradients cannot be explained solely by dust
and are indicative of changes in the mix of stellar ages and/or metallicity as
a function of both radius and height above the galaxy plane. The outer regions
of the UGC7321 disk are too blue to be explained by low metallicity alone
(B-R<0.6), and must be relatively young. However, the galaxy also contains
stellar populations with B-R>1.1, indicating it is not a young or
recently-formed galaxy. The disk of UGC7321 is not a simple exponential, but
exhibits a light excess at small radii, as well as distinct surface brightness
zones. Together the properties of UGC7321 imply that it is an under-evolved
galaxy in both a dynamical and in a star-formation sense. (Abridged)Comment: Accepted to the Astronomical Journal; 28 pages, 1 table and 21
figures (GIF and postscript
The u'g'r'i'z' Standard Star Network
We present the 158 standard stars that define the u'g'r'i'z' photometric
system. These stars form the basis for the photometric calibration of the Sloan
Digital Sky Survey (SDSS). The defining instrument system and filters, the
observing process, the reduction techniques, and the software used to create
the stellar network are all described. We briefly discuss the history of the
star selection process, the derivation of a set of transformation equations for
the UBVRcIc system, and plans for future work.Comment: References to URLs in paper have been updated to reflect moved
website. Accepted by AJ. 50 pages, including 20 pages of text, 9 tables, and
15 figures. Plain ASCII text versions of Tables 8 and 9 can be found at
http://home.fnal.gov/~dtucker/ugriz/index.html (new URL
The Updated Zwicky Catalog (UZC)
The Zwicky Catalog of galaxies (ZC), with m_Zw<=15.5mag, has been the basis
for the Center for Astrophysics (CfA) redshift surveys. To date, analyses of
the ZC and redshift surveys based on it have relied on heterogeneous sets of
galaxy coordinates and redshifts. Here we correct some of the inadequacies of
previous catalogs by providing: (1) coordinates with <~2 arcsec errors for all
of the Nuzc catalog galaxies, (2) homogeneously estimated redshifts for the
majority (98%) of the data taken at the CfA (14,632 spectra), and (3) an
estimate of the remaining "blunder" rate for both the CfA redshifts and for
those compiled from the literature. For the reanalyzed CfA data we include a
calibrated, uniformly determined error and an indication of the presence of
emission lines in each spectrum. We provide redshifts for 7,257 galaxies in the
CfA2 redshift survey not previously published; for another 5,625 CfA redshifts
we list the remeasured or uniformly re-reduced value. Among our new
measurements, Nmul are members of UZC "multiplets" associated with the original
Zwicky catalog position in the coordinate range where the catalog is 98%
complete. These multiplets provide new candidates for examination of tidal
interactions among galaxies. All of the new redshifts correspond to UZC
galaxies with properties recorded in the CfA redshift compilation known as
ZCAT. About 1,000 of our new measurements were motivated either by inadequate
signal-to-noise in the original spectrum or by an ambiguous identification of
the galaxy associated with a ZCAT redshift. The redshift catalog we include
here is ~96% complete to m_Zw<=15.5, and ~98% complete (12,925 galaxies out of
a total of 13,150) for the RA(1950) ranges [20h--4h] and [8h--17h] and
DEC(1950) range [-2.5d--50d]. (abridged)Comment: 34 pp, 7 figs, PASP 1999, 111, 43
Planetary Nebulae as Standard Candles. XII. Connecting the Population I and Population II Distance Scales
We report the results of [OIII] lambda 5007 surveys for planetary nebulae
(PNe) in NGC 2403, 3115, 3351, 3627, 4258, and 5866. Using on-band/off-band
[OIII] and H-alpha images, we identify samples of PNe in these galaxies and
derive distances using the planetary nebula luminosity function (PNLF). We then
combine these measurements with previous data to compare the PNLF, Cepheid, and
surface brightness fluctuation (SBF) distance scales. We use a sample of 13
galaxies to show that the absolute magnitude of the PNLF cutoff is fainter in
small, low-metallicity systems, but the trend is well modelled theoretically.
When this dependence is removed, the scatter between the Cepheid and PNLF
distances becomes consistent with the internal errors of the methods and
independent of any obvious galaxy parameter. We then use the data to
recalibrate the zero point of the PNLF distance scale. We use a sample of 28
galaxies to show that the scatter between the PNLF and SBF distance
measurements agrees with that predicted from the techniques' internal errors,
and that no systematic trend exists between the distance residuals and stellar
population. However, we find the PNLF and SBF methods have a significant scale
offset: Cepheid-calibrated PNLF distances are, on average, ~0.3 mag smaller
than Cepheid-calibrated SBF distances. We discuss the possible causes of this
offset, and suggest that internal extinction in the bulges of the SBF
calibration galaxies is the principle cause of the discrepancy. If this is
correct, the SBF-based Hubble Constant must be increased by ~7%. We use our
distance to NGC 4258 to argue that the short distance scale to the LMC is
correct, and that the global Hubble Constant inferred from the HST Key Project
should be increased by 8 +/- 3% to H_0 = 78 +/- 7 km/s/Mpc. (abridged)Comment: 38 pages, 9 figures included, accepted for publication in the
Astrophysical Journa
Data and 2D scaling relations for galaxies in Abell 1689: a hint of size evolution at z~0.2
{abridged} We present imaging and spectroscopy of Abell 1689 (z=0.183) from
GEMINI/GMOS-N and HST/ACS. We measure integrated photometry from the GMOS g'
and r' images (for 531 galaxies) and surface photometry from the HST F625W
image (for 43 galaxies) as well as velocities and velocity dispersions from the
GMOS spectra (for 71 galaxies). We construct the Kormendy relation (KR),
Faber-Jackson relation (FJR) and colour-magnitude relation (CMR) for early-type
galaxies in Abell 1689 using this data and compare them to those of the Coma
cluster. We measure the intrinsic scatter of the CMR in Abell 1689 to be 0.054
\pm 0.004 mag which places degenerate constraints on the ratio of the assembly
timescale to the time available (beta) and the age of the population. Making
the assumption that galaxies in Abell 1689 will evolve into those of Coma over
an interval of 2.26 Gyr breaks this degeneracy and limits beta to be > 0.6 and
the age of the red sequence to be > 5.5 Gyr (formed at z > 0.55). Without
corrections for size evolution but accounting for magnitude cuts and selection
effects, the KR & FJR are inconsistent and disagree at the 2 sigma level
regarding the amount of luminosity evolution in the last 2.26 Gyr. However,
after correcting for size evolution the KR & FJR show similar changes in
luminosity (0.22 \pm 0.11 mag) that are consistent with the passive evolution
of the stellar populations from a single burst of star formation 10.2 \pm 3.3
Gyr ago (z = 1.8+inf-0.9). Thus the changes in the KR, FJR & CMR of Abell 1689
relative to Coma all agree and suggest old galaxy populations with little or no
synchronisation in the star formation histories. Furthermore, the weak evidence
for size evolution in the cluster environment in the last 2.26 Gyr places
interesting constraints on the possible mechanisms at work, favouring
harassment or secular processes over merger scenarios.Comment: Accepted for publication in MNRA
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