Puragra Guhathakurta

Science Objectives and Early Results of the DEEP2 Redshift Survey

The DEIMOS spectrograph has now been installed on the Keck-II telescope and commissioning is nearly complete. The DEEP2 Redshift Survey, which will take approximately 120 nights at the Keck Observatory over a three year period and has been designed to utilize the power of DEIMOS, began in the summer of 2002. The multiplexing power and high efficiency of DEIMOS enables us to target 1000 faint galaxies per clear night. Our goal is to gather high-quality spectra of ≈ 60,000 galaxies with z>0.75 in order to study the properties and large scale clustering of galaxies at z ≈ 1. The survey will be executed at high spectral resolution, R=λ/Δλ ≈ 5000, allowing us to work between the bright OH sky emission lines and to infer linewidths for many of the target galaxies (for several thousand objects, we will obtain rotation curves as well). The linewidth data will facilitate the execution of the classical redshift-volume cosmological test, which can provide a precision measurement of the equation of state of the Universe. This talk reviews the project, summarizes our science goals and presents some early DEIMOS data.

Absence of evidence is not evidence of absence: the colour–density relation at fixed stellar mass persists to z∼ 1

We use data drawn from the DEEP2 Galaxy Redshift Survey to investigate the relationship between local galaxy density, stellar mass and rest-frame galaxy colour. At z∼ 0.9, we find that the shape of the stellar mass function at the high-mass [ log 10(M*/h−2xa0 M⊙) > 10.1] end depends on the local environment, with high-density regions favouring more massive systems. Accounting for this stellar mass–environment relation (i.e. working at fixed stellar mass), we find a significant colour–density relation for galaxies with 10.6 1.

Keck studies of M31's stellar halo

We present Keck 10-meter/LRIS spectra of candidate red giants in the halo of M31, located at a projected radius of R equals 19kpc on the minor axis. These spectroscopic targets have been selected using a combination of UBRI-based and morphological screening to eliminate background galaxies. Radial velocity measurements are used to separate M312 halo giants from foreground Milky Way dwarf stars, M31 disk stars, and residual background galaxies. The metallicity of each M31 halo giant is measured using standard photometric and spectroscopic techniques, the latter based on the strength of the Ca II triplet. The various (Fe/H) estimates are in rough agreement with one another. The data reveal a large spread in (Fe/H) in M31s halo; there is no strong radial (Fe/H) gradient. LRIS and HIRES spectra are also presented for red giants in five dwarf spheroidal satellites of M31: AndI, AndIII, AndV, AndVI, and AndVII. There appears to be a significant metallicity spread in AndVI and possibly in AndI. The new radial velocity data on these outer dwarfs are used to constrain the total mass of M31: the best estimate in under 1012 M, somewhat less than the best estimate for the Milky Way.

How Good Is the Near-Infrared Tully-Fisher Relation?

A study of the Tully-Fisher relation (TFR) in H, I, and B filter bands using high-quality data for 25 Coma-region spirals confirms the common suspicion that the infrared TFRs have lower scatter than the blue TFR. We find, however, that the I-band TFR has equivalent or slightly lower scatter (0.10 mag RMS!) than the H-band TFR, and that internal extinction corrections are important even in H band, so that infrared array detectors offer little advantage over I-band CCD data for TFR surveys. Extensions to the 25-galaxy sample, and comparisons with other authors, show that there are spirals which depart by 1 mag or more from the original infrared TFR, and that the slope of the TFR may vary. There are hints that I - H colors may be useful in detecting and diagnosing the differences between spirals which have common rotation speeds yet have up to threefold discrepancies in infrared luminosity.