17 May 2001CfA Colloquium


Title: Search Techniques and Some Results on Distant Galaxies

Speaker: Hy Spinrad

Abstract: Locating and studying young galaxies at z >3 is an important base toward our understanding of galaxy formation.

I'll review successful and partly successful methods to locate the few and faint populations of very distant systems; we now (with difficulty) observe a few galaxies within about 1.5 Gyrs of the Big Bang.

I will detail the comparison between photometrically selected high-redshift candidates and the galaxies detected by Ly-alpha imaging searches and the Lyman-alpha detections of SERendip line emitters.

To my surprise, the morphologies of HDF-chosen galaxies seem equally peculiar at z ~ 1.0 [half-way back in time] and at z = 4.5 (> 80% back). Mergers must be important at both epochs.

Mass ejection is apparently common at "early galaxy times"; I will illustrate with one nice and new Ly-alpha profile and some model fits to it. This SERendip galaxy (z = 5.189) has a broad emission-line red edge symptomatic of a velocity field reaching over 500 kms-1. This is much greater than Vesc from a small galaxy.

Finally, it is probably possible to determine heavy-element abundances in some (relatively bright) active star-forming galaxies at z ~ 3. We note initially a coarse set of correlations between the strength of Ly-alpha emission, the slope of the continuum longward of Ly-alpha, and the E.W.'s of the UV absorption lines of SiII, and CII, and OI. I have attempted to convert the line strengths to metal abundances; in the most metal-poor case, with fair spectroscopic evidence, I deduce an interstellar metalicity of about 1/60 solar. Most of the Ly-break galxies are modestly sub-solar.

Reference for students:

"Search Techniques for Distant Galaxies" Stern & Spinrad, 1999, PASP 11, 1475

Lunch with the students will be on Friday, May 18th at 12:00 in A-101.