1,107 research outputs found
Spectral Analysis of the Stromlo-APM Survey II. Galaxy luminosity function and clustering by spectral type
We study the luminosity function and clustering properties of subsamples of
local galaxies selected from the Stromlo-APM survey by the rest-frame
equivalent widths of their Halpha and Oii emission lines. The b_J luminosity
function of star-forming galaxies has a significantly steeper faint-end slope
than that for quiescent galaxies: the majority of sub-L* galaxies are currently
undergoing significant star formation. Emission line galaxies are less strongly
clustered, both amongst themselves, and with the general galaxy population,
than quiescent galaxies. Thus as well as being less luminous, star-forming
galaxies also inhabit lower-density regions of the Universe than quiescent
galaxies.Comment: 8 pages, 7 figures, MNRAS, in pres
Spectral Analysis of the Stromlo-APM Survey I. Spectral Properties of Galaxies
We analyze spectral properties of 1671 galaxies from the Stromlo-APM survey,
selected to have 15 < b_J < 17.15 and having a mean redshift z = 0.05. This is
a representative local sample of field galaxies, so the global properties of
the galaxy population provide a comparative point for analysis of more distant
surveys. We measure Halpha, Oii 3727, Sii 6716, 6731, Nii 6583 and Oi 6300
equivalent widths and the D_4000 break index. The 5A resolution spectra use an
8 arcsec slit, which typically covers 40-50% of the galaxy area. We find no
evidence for systematic trends depending on the fraction of galaxy covered by
the slit, and further analysis suggests that our spectra are representative of
integrated galaxy spectra.
We classify spectra according to their Halpha emission, which is closely
related to massive star formation. Overall we find 61% of galaxies are Halpha
emitters with rest-frame equivalent widths EW(Halpha) >= 2A. The emission-line
galaxy (ELG) fraction is smaller than seen in the CFRS at z = 0.2 and is
consistent with a rapid evolution of Halpha luminosity density. The ELG
fraction, and EW(Halpha), increase at fainter absolute magnitudes, smaller
projected area and smaller D_4000. In the local Universe, faint, small galaxies
are dominated by star formation activity, while bright, large galaxies are more
quiescent. This picture of the local Universe is quite different from the
distant one, where bright galaxies appear to show rapidly-increasing activity
back in time.
(Abridged)Comment: 40 pages, 25 figures, MNRAS, in pres
The Ha Luminosity Function and Star Formation Rate at z\sim 0.2
We have measured the Ha+[N II] fluxes of the I-selected Canada-France
Redshift Survey (CFRS) galaxies lying at a redshift z below 0.3, and hence
derived the Ha luminosity function. The magnitude limits of the CFRS mean that
only the galaxies with M(B) > -21 mag were observed at these redshifts. We
obtained a total Ha luminosity density of at least 10^{39.44\pm 0.04}
erg/s/Mpc^{3} at a mean z=0.2 for galaxies with rest-fame EW(Ha+[N II]) > 10
Angs. This is twice the value found in the local universe by Gallego et al.
1995. Our Ha star formation rate, derived from Madau (1997) is higher than the
UV observations at same z, implying a UV dust extinction of about 1 mag. We
found a strong correlation between the Ha luminosity and the absolute magnitude
in the B-band: M(B(AB)) = 46.7 - 1.6 log L(Ha). This work will serve as a basis
of future studies of Ha luminosity distributions measured from
optically-selected spectroscopic surveys of the distant universe, and it will
provide a better understanding of the physical processes responsible for the
observed galaxy evolution.Comment: Accepted for publication in ApJ, 14 pages, LaTeX (macro aas2pp4.sty),
6 figure
The Ha luminosity function and star formation rate up to z~1
We describe ISAAC/ESO-VLT observations of the Ha(6563) Balmer line of 33
field galaxies from the Canada-France Redshift Survey (CFRS) with redshifts
selected between 0.5 and 1.1. We detect Ha in emission in 30 galaxies and
compare the properties of this sample with the low-redshift sample of CFRS
galaxies at z~0.2 (Tresse & Maddox 1998). We find that the Ha luminosity,
L(Ha), is tightly correlated to M(B(AB)) in the same way for both the low- and
high-redshift samples. L(Ha) is also correlated to L([OII]3727), and again the
relation appears to be similar at low and high redshifts. The ratio
L([OII])/L(Ha) decreases for brighter galaxies by as much as a factor 2 on
average. Derived from the Ha luminosity function, the comoving Ha luminosity
density increases by a factor 12 from =0.2 to =1.3. Our results confirm a
strong rise of the star formation rate (SFR) at z<1.3, proportional to
(1+z)^{4.1+/-0.3} (with H_0=50 km/s/Mpc, q_0=0.5). We find an average SFR(2800
Ang)/SFR(Ha) ratio of 3.2 using the Kennicutt (1998) SFR transformations. This
corresponds to the dust correction that is required to make the near UV data
consistent with the reddening-corrected Ha data within the self-contained,
I-selected CFRS sample.Comment: 16 pages, 16 figures and 3 tables included, figures and text updated,
same results as in the 1st version, accepted in MNRA
The CANADA-FRANCE REDSHIFT SURVEY I: Introduction to the Survey, Photometric Catalogs and Surface Brightness Selection Effects
The Canada-France Redshift Survey has been undertaken to provide a large
well-defined sample of faint galaxies at high redshift in which the selection
criteria match as closely as possible those of samples of nearby galaxies. The
survey is designed to have a median redshift of z ~ 0.6 corresponding to a
look-back time of half the present age of the Universe for Omega ~ 1. Such a
survey can then be used for studying many different aspects of the evolution of
galaxies over the interval 0 < z < 1. In this paper we describe the selection
of the fields, the multicolor imaging observations and the construction and
validation of the photometric catalogs. Particular attention is paid to
quantifying the unavoidable selection effects in surface brightness and their
impact on the survey is assessed in the context of the properties of known
populations of galaxies. The photometric catalogs contain several thousand
objects brighter than I_{AB}< 22.5 and are essentially complete for central
surface brightnesses as faint as 24.5 mag arcsec.
This should be sufficient to include both normal surface brightness galaxies
and prototypes of extreme low surface brightness galaxies.Comment: 17 pages, 2 tables, 10 postscript figures (in 2 parts), uses
aaspp.sty Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.html
and coming soon on a CFRS homepag
THE CANADA-FRANCE REDSHIFT SURVEY II: Spectroscopic Program; Data for the 0000-00 and 1000+25 Fields
This paper describes the methods used to obtain the spectroscopic data and
construct redshift catalogs for the Canada-France deep Redshift Survey (CFRS).
The full data set consists of more than one thousand spectra, of objects with
17.5 < I_{AB} < 22.5, obtained from deep multi-slit data with the MARLIN and
MOS-SIS spectrographs at the CFHT. The final spectroscopic catalog contains 200
stars, 591 galaxies with secure redshifts in the range 0 < z < 1.3, 6 QSOs, and
146 objects with very uncertain or unknown redshifts, leading to an overall
success rate of identification of 85%. Additionally, 67 objects affected by
observational problems have been placed in a supplemental list.
We describe here the instrumental set up, and the observing procedures used
to efficiently gather this large data set. New optimal ways of packing spectra
on the detector to significantly increase the multiplexing gain offered by
multi-slit spectroscopy are described. Dedicated data reduction procedures have
been developed under the IRAF environment to allow for fast and accurate
processing.
Very strict procedures have been followed to establish a reliable list of
final spectroscopic measurements. Fully independent processing of the data has
been carried out by three members of the team for each data set associated with
a multi-slit mask, and final redshifts were
assigned only after the careful comparison of the three independent
measurements. A confidence class scheme was established. We strongly emphasize
the benefits of such procedures.
Finally, we present the spectroscopic data obtained for 303 objects in the
0000-00 and 1000+25 fields. The success rate in spectroscopic identification isComment: 16 uuencoded postcript pages with figures 4,5,8,9 and 12. Other
(large) figures available from the authors. Large data table not yet
released. Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.html
and coming soon on a CFRS homepage. Accepted June 19, scheduled for the Dec
10 issue of Ap
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