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.