Measuring Feedback in Damped Lyman Alpha Systems

We measure feedback (heating rates) in damped Lyman alpha systems from the cooling rate of the neutral gas. Since cooling occurs through [C II] 158 micron emission, we infer cooling from C II^{*} 1335.7 absorption lines detected with HIRES on the Keck I telescope. The inferred heating rates are about 30 times lower than for the Galaxy ISM. At z = 2.8, the implied star formation rate per unit area is 10^{-2.4+-0.3} solar masses per kpc^{2} per year, and the the star formation rate per unit comoving volume is 10^{-0.8+-0.2} solar masses per Mpc^{3} per year. This is the first measurement of star formation rates in objects likely to be the progenitors of current galaxies.Comment: 7 pages, 5 figures, Proceedings of the ESO/ECF/STScI Workshop on Deep Field

Are Simulations of CDM Consistent with Galactic-Scale Observations at High Redshift?

We compare new observations on the kinematic characteristics of the damped Lya systems against results from numerical SPH simulations to test the predictions of hierarchical galaxy formation. This exercise is particularly motivated by recent numerical results on the cross-section of damped Lya systems. Our analysis focuses on the velocity widths of ~50 low-ion absorption profiles from our sample of z>1.5 damped Lya systems. The results indicate that current numerical simulations fail to match the damped Lya observations at high confidence levels (>99.9%). Although we do not believe that our results present an insurmountable challenge to the paradigm of hierarchical cosmology, the damped Lya observations suggest that current numerical SPH simulations overlook an integral aspect of galaxy formation.Comment: 4 pages, 2 color figures; Submitted to ApJ

A Keck HIRES Investigation of the Metal Abundances and Kinematics of the z=2.46 Damped Lya System Toward Q0201+365

We present high resolution ($\approx 8$ \kms) spectra of the QSO Q0201+365 obtained with HIRES, the echelle spectrograph on the 10m W.M. Keck Telescope. Although we identify over $80\%$ of the absorption features and analyze several of the more complex metal-line systems, we focus our analysis on the damped \Lya system at $z=2.462$. Ionization simulations suggest the hydrogen in this system is significantly neutral and all of the observed metals are predominantly singly ionized. We measure accurate abundances for Fe, Cr, Si, Ni and place a lower limit on the abundance of Zn: [Fe/H] = $-0.830 \pm 0.051$, [Cr/H] = $-0.902 \pm 0.064$, [Si/H] = $-0.376 \pm 0.052$, [Ni/H] = $-1.002 \pm 0.054$ and [Zn/H] $> -0.562 \pm 0.064$. We give evidence suggesting the actual Zn abundance is [Zn/H] $\approx -0.262$, implying the highest metallicity observed at a redshift $z \geq 2$. The relative abundances of these elements remains constant over essentially the entire system ($\approx 150$ \kms in velocity space), suggesting it is well mixed. Furthermore, we use the lack of abundance variations to infer properties of the dust responsible for element depletion. Finally, we discuss the kinematic characteristics of this damped \Lya system, comparing and contrasting it with other systems. The low-ion line profiles span $\approx 200$ \kms in velocity space and have an asymmetric shape with the strongest feature on the red edge. These kinematic characteristics are consistent with a rotating disk model.Comment: 60 pages, 20 encapsulated figures, uses aaspp4.sty. Also available at http://nately.ucsd.edu/~xavier/DLA/obs.htm