Spitzer Warm Mission Workshop Introduction

The Spitzer Warm Mission Workshop was held June 4–5, 2007, to explore the science drivers for the warm Spitzer mission and help the Spitzer Science Center develop a new science operations philosophy. We must continue to maximize the science return with the reduced resources available, both using (a) the shortest two IRAC channels, and (b) archival research with the rich Spitzer archive. This paper summarizes the overview slides presented to the workshop participant

Microlens Parallax Measurements with a Warm Spitzer

Because Spitzer is an Earth-trailing orbit, losing about 0.1 AU/yr, it is excellently located to perform microlens parallax observations toward the Magellanic Clouds (LMC/SMC) and the Galactic bulge. These yield the so-called ``projected velocity'' of the lens, which can distinguish statistically among different populations. A few such measurements toward the LMC/SMC would reveal the nature of the lenses being detected in this direction (dark halo objects, or ordinary LMC/SMC stars). Cool Spitzer has already made one such measurement of a (rare) bright red-clump source, but warm (presumably less oversubscribed) Spitzer could devote the extra time required to obtain microlens parallaxes for the more common, but fainter, turnoff sources. Warm Spitzer could observe bulge microlenses for 38 days per year, which would permit up to 24 microlens parallaxes per year. This would yield interesting information on the disk mass function, particularly old brown dwarfs, which at present are inaccessible by other techniques. Target-of-Opportunity (TOO) observations should be divided into RTOO/DTOO, i.e., ``regular'' and ``disruptive'' TOOs, as pioneered by the Space Interferometry Mission (SIM). LMC/SMC parallax measurements would be DTOO, but bulge measurements would be RTOO, i.e., they could be scheduled in advance, without knowing exactly which star was to be observed.Comment: 6 pages + 1 Figure, To be presented at The Warm Spitzer Mission Workshop, 4-5 June 2007, Pasaden

NICMOS Snapshot Survey of Damped Lyman Alpha Quasars

We image 19 quasars with 22 damped Lyman alpha (DLA) systems using the F160W filter and the Near-Infrared Camera and Multiobject Spectrograph aboard the Hubble Space Telescope, in both direct and coronagraphic modes. We reach 5 sigma detection limits of ~H=22 in the majority of our images. We compare our observations to the observed Lyman-break population of high-redshift galaxies, as well as Bruzual & Charlot evolutionary models of present-day galaxies redshifted to the distances of the absorption systems. We predict H magnitudes for our DLAs, assuming they are producing stars like an L* Lyman-break galaxy (LBG) at their redshift. Comparing these predictions to our sensitivity, we find that we should be able to detect a galaxy around 0.5-1.0 L* (LBG) for most of our observations. We find only one new possible candidate, that near LBQS0010-0012. This scarcity of candidates leads us to the conclusion that most DLA systems are not drawn from a normal LBG luminosity function nor a local galaxy luminosity function placed at these high redshifts.Comment: 31 pages, 8 figures, Accepted for Feb. 10 issue of Ap

Mid-infrared selection of quasar-2s in Spitzer's First Look Survey

We present early results from the spectroscopic follow-up of a sample of candidate obscured AGN selected in the mid-infrared from the Spitzer First Look Survey. Our selection allows a direct comparison of the numbers of obscured and unobscured AGN at a given luminosity for the first time, and shows that the ratio of obscured to unobscured AGN at infrared luminosities corresponding to low luminosity quasars is ~1:1 at z~0.5. Most of our optically-faint candidate obscured AGN have the high-ionization, narrow-line spectra expected from type-2 AGN. A composite spectrum shows evidence for Balmer absorption lines, indicating recent star-formation activity in the host galaxies. There is tentative evidence for a decrease in the obscured AGN fraction with increasing AGN luminosity.Comment: To appear in the proceedings of the workshop "Multiband approach to AGN" Bonn October 2004 in Memorie della Societa Astronomica Italian

Simulations of Damped Lyman-Alpha and Lyman Limit Absorbers in Different Cosmologies: Implications for Structure Formation at High Redshift

We use hydrodynamic cosmological simulations to study damped Lyman-alpha (DLA) and Lyman limit (LL) absorption at redshifts z=2-4 in five variants of the cold dark matter scenario. Our standard simulations resolve the formation of dense concentrations of neutral gas in halos with circular velocity v_c roughly 140 km/s for Omega_m=1 and 90 km/s for Omega_m=0.4, at z=2; an additional LCDM simulation resolves halos down to v_c approximately 50 km/s at z=3. We find a clear relation between HI column density and projected distance to the center of the nearest galaxy, with DLA absorption usually confined to galactocentric radii less than 10-15 kpc and LL absorption arising out to projected separations of 30 kpc or more. Detailed examination provides evidence of non-equilibrium effects on absorption cross-section. If we consider only absorption in the halos resolved by our standard simulations, then all five models fall short of reproducing the observed abundance of DLA and LL systems at these redshifts. If we extrapolate to lower halo masses, we find all four models are consistent with the observed abundance of DLA systems if the the extrapolated behavior extends to circular velocities roughly 50-80 km/s, and they may produce too much absorption if the relation continues to 40 km/s. Our results suggest that LL absorption is closely akin to DLA absorption, arising in less massive halos or at larger galactocentric radii but not caused by processes acting on a radically different mass scale.Comment: 33 pages with 10 embedded EPS figures. Substantially revised and updated from original version. Includes new high-resolution simulations. Accepted for publication in the Ap

Approaches to Automated Morphological Classification of Galaxies

There is an obvious need for automated classification of galaxies, as the number of observed galaxies increases very fast. We examine several approaches to this problem, utilising {\em Artificial Neural Networks} (ANNs). We quote results from a recent study which show that ANNs can classsify galaxies morphologically as well as humans can.Comment: 8 pages, uu-encoded compressed postscript file (containing 2 figures