A deep redshift survey of field galaxies. Comments on the reality of the Butcher-Oemler effect

A spectroscopic survey of over 400 field galaxies has been completed in three fields for which we have deep UBVI photographic photometry. The galaxies typically range from B=20 to 22 and possess redshifts z from 0.1 to 0.5 that are often quite spiky in distribution. Little, if any, luminosity evolution is observed up to redshifts z approx 0.5. By such redshifts, however, an unexpectedly large fraction of luminous galaxies has very blue intrinsic colors that suggest extensive star formation; in contrast, the reddest galaxies still have colors that match those of present-day ellipticals

HST Observations of the Distant Cluster 0016+16: Quantitative Morphology of Confirmed Cluster Members

We present HST images of 24 confirmed members of the distant galaxy cluster Cl0016+16 at redshift 0.55. The Balmer-strong (``E+A'') and emission- line galaxies frequently show unusual visual morphology, implying that galaxian interactions produce ``active'' galaxies in moderate-redshift clusters. We use the image concentration index as a quantitative measure of morphology to show that these unusual galaxies appear disklike, while the normal red galaxies resemble E/S0s. Although consistent with HST observations by Dressler et al. in Cl0939+4713 ($z=0.41$), our results differ from the Couch et al. finding that most Balmer-strong galaxies in AC114 ($z=0.31$) resemble ellipticals. The entire ``E+A'' sample is small, but if future studies confirm their diversity, it will suggest that they have different origins.Comment: 11 pages, uuencoded compressed PostScript, accepted to ApJ Letters, LICK-3

Continuum Variability of Active Galactic Nuclei in the Optical-Ultraviolet Range

The variability of the continuum spectral energy distribution has been analyzed for a complete magnitude-limited sample of quasars in Selected Area 57, observed at two epochs in the photographic U, BJ, F, and N bands with the Mayall 4 m telescope at Kitt Peak National Observatory. Changes δα of the spectral slope α appear correlated with brightness variations δ log fν, indicating an average hardening of the spectrum in the bright phases. This confirms that the correlation of variability with redshift, found in a single observing band, is due to intrinsic spectral changes. The average observed δα-δ log fν relation is consistent with the spectral change due to temperature variation of a blackbody of about 2.5 × 104 K

The Luminosity Function for L>L* Galaxies at z > 3

Through use of multiband (U, B, R, I) photometry we have isolated high redshift (3.0<z<3.5) galaxy candidates in a survey of 1.27 deg^2 to R = 21.25 and a survey of 0.02 deg^2 to R = 23.5. Our pool of candidates constrains the nature of the 3.0 < z < 3.5 luminosity function over the range L* < L < 100 L*, if we grant a similar level of completeness to these data as for very faint samples (to R = 25.5) selected in a similar fashion. Our constraints agree with the high redshift sky density at R = 20.5 estimated from Yee et al.'s (1996) serendipitous discovery of a bright, z = 2.7 galaxy, as well as the density at R ~ 23 by Steidel et al. (1996b). We strongly rule out -- by more than two orders of magnitude at M(R) = -25 -- the L > L* luminosity function for z = 3-5 galaxies obtained by a photometric redshift analysis of the Hubble Deep Field (HDF) by Gwyn & Hartwick (1996). Our results at R ~ 23 are more consistent with the photometric redshift analysis of the faint HDF galaxies by Sawicki & Yee (1996), but our present upper limits at the brightest magnitudes (R < 21.5, M(R) < -24) allow more generous volume densities of these super-L* galaxies.Comment: Accepted for publication in ApJ Letters; 14 pages Latex, including 3 figure

Survey incompleteness and the evolution of the QSO luminosity function

We concentrate on a type of QSO survey which depends on selecting QSO candidates based on combinations of colors. Since QSO's have emission lines and power-law continua, they are expected to yield broadband colors unlike those of stellar photospheres. Previously, the fraction of QSO's expected to be hiding (unselected) within the locus of stellar (U-J, J-F) colors was estimated at about 15 percent. We have now verified that the KK88 survey is at least 11 percent incomplete, but have determined that it may be as much as 34 percent incomplete. The 'missing' QSO's are expected to be predominantly at z less than or = 2.2. We have studied the proper motion and variability properties of all stellar objects with J less than or = 22.5 or F less than or = 21.5 in the SA 57 field which has previously been surveyed with a multicolor QSO search by KK88

The DESI Experiment, a whitepaper for Snowmass 2013

The Dark Energy Spectroscopic Instrument (DESI) is a massively multiplexed fiber-fed spectrograph that will make the next major advance in dark energy in the timeframe 2018-2022. On the Mayall telescope, DESI will obtain spectra and redshifts for at least 18 million emission-line galaxies, 4 million luminous red galaxies and 3 million quasi-stellar objects, in order to: probe the effects of dark energy on the expansion history using baryon acoustic oscillations (BAO), measure the gravitational growth history through redshift-space distortions, measure the sum of neutrino masses, and investigate the signatures of primordial inflation. The resulting 3-D galaxy maps at z<2 and Lyman-alpha forest at z>2 will make 1%-level measurements of the distance scale in 35 redshift bins, thus providing unprecedented constraints on cosmological models.Comment: 14 pages, 4 figures, a White Paper for Snowmass 201

Characteristic QSO Accretion Disk Temperatures from Spectroscopic Continuum Variability

Using Sloan Digital Sky Survey (SDSS) quasar spectra taken at multiple epochs, we find that the composite flux density differences in the rest frame wavelength range 1300-6000 AA can be fit by a standard thermal accretion disk model where the accretion rate has changed from one epoch to the next (without considering additional continuum emission components). The fit to the composite residual has two free parameters: a normalizing constant and the average characteristic temperature $\bar{T}^*$. In turn the characteristic temperature is dependent on the ratio of the mass accretion rate to the square of the black hole mass. We therefore conclude that most of the UV/optical variability may be due to processes involving the disk, and thus that a significant fraction of the UV/optical spectrum may come directly from the disk.Comment: 31 pages, 8 figure

Star Clusters in the Nearby Late-Type Galaxy NGC 1311

Ultraviolet, optical and near infrared images of the nearby (D ~ 5.5 Mpc) SBm galaxy NGC 1311, obtained with the Hubble Space Telescope, reveal a small population of 13 candidate star clusters. We identify candidate star clusters based on a combination of their luminosity, extent and spectral energy distribution. The masses of the cluster candidates range from ~1000 up to ~100000 Solar masses, and show a strong positive trend of larger mass with increasing with cluster age. Such a trend follows from the fading and dissolution of old, low-mass clusters, and the lack of any young super star clusters of the sort often formed in strong starbursts. The cluster age distribution is consistent with a bursting mode of cluster formation, with active episodes of age ~10 Myr, ~100 Myr and ~1 Gyr. The ranges of age and mass we probe are consistent with those of the star clusters found in quiescent Local Group dwarf galaxies.Comment: 21 pages, 11 figures, accepted by A