3 research outputs found
The Evolution of Early-type Field Galaxies Selected from a NICMOS Map of the Hubble Deep Field North
The redshift distribution of well-defined samples of distant early-type
galaxies offers a means to test the predictions of monolithic and hierarchical
galaxy formation scenarios. NICMOS maps of the entire Hubble Deep Field North
in the F110W and F160W filters, when combined with the available WFPC2 data,
allow us to calculate photometric redshifts and determine the morphological
appearance of galaxies at rest-frame optical wavelengths out to z ~ 2.5. Here
we report results for two subsamples of early-type galaxies, defined primarily
by their morphologies in the F160W band, which were selected from the NICMOS
data down to H160_{AB} < 24.0. The observed redshift distributions of our two
early-type samples do not match that predicted by a monolithic collapse model,
which shows an overabundance at z > 1.5. A hierarchical formation model better
matches the redshift distribution of the HDF-N early-types at z > 1.5, but
still does not adequately describe the observed early-types. The hierarchical
model predicts significantly bluer colors on average than the observed
early-type colors, and underpredicts the observed number of early-types at z <
1. [abridged]Comment: Accepted for publication in the Astronomical Journal; 54 pages, 21
figures. Figures 10 and 11 are included separately in JPEG forma
Red and Reddened Quasars in the Sloan Digital Sky Survey
We investigate the continuum and emission line properties of 4576 SDSS
quasars as a function of their optical/UV SEDs. The optical/UV color
distribution of our sample is roughly Gaussian, but with a red tail; we
distinguish between 1) intrinsically blue (optically flat) quasars, 2)
intrinsically red (optically steep) quasars, and 3) the 273 (6%) of our quasars
whose continua are inconsistent with a single power-law and appear redder due
to SMC-like dust reddening rather than synchrotron emission. The color
distribution suggests that the population of moderately dust reddened
broad-line quasars is smaller than that of unobscured quasars, but we estimate
that a further 10% of the luminous quasar population is missing from the SDSS
sample because of dust extinction with E(B-V)<0.5. We also investigate the
emission and absorption line properties of these quasars as a function of color
with regard to Boroson & Green type eigenvectors. Intrinsically red (optically
steep) quasars tend to have narrower Balmer lines and weaker CIV, CIII], HeII
and 3000A bump emission as compared with bluer (optically flatter) quasars. The
change in strength of the 3000A bump appears to be dominated by the Balmer
continuum and not by FeII emission. The dust reddened quasars have even
narrower Balmer lines and weaker 3000A bumps, in addition to having
considerably larger equivalent widths of [OII] and [OIII] emission. The
fraction of broad absorption line quasars (BALQSOs) increases from ~3.4% for
the bluest quasars to perhaps as large as 20% for the dust reddened quasars,
but the intrinsic color distribution is affected by dust reddening. (abridged)Comment: 37 pages, 10 figures (3 color), 2 tables, accepted by AJ. For a
version with higher quality figures, see
ftp://astro.princeton.edu/gtr/redqsos/RichardsGT_redqsos.revised3.preprint.p
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The First Data Release of the Sloan Digital Sky Survey
The Sloan Digital Sky Survey (SDSS) has validated and made publicly available its First Data Release. This consists of 2099 deg2 of five-band (u, g, r, i, z) imaging data, 186,240 spectra of galaxies, quasars, stars and calibrating blank sky patches selected over 1360 deg2 of this area, and tables of measured parameters from these data. The imaging data go to a depth of r ≈ 22.6 and are photometrically and astrometrically calibrated to 2% rms and 100 mas rms per coordinate, respectively. The spectra cover the range 3800–9200 Å, with a resolution of 1800–2100. This paper describes the characteristics of the data with emphasis on improvements since the release of commissioning data (the SDSS Early Data Release) and serves as a pointer to extensive published and on-line documentation of the survey.Astronom