Published in "The Hubble Deep Field", eds. M. Livio, S.M. Fall and P. Madau 1998
B
29m,
AND GALAXY FORMATION FROM SUB-GALACTIC CLUMPS2 Dept. of Physics & Astronomy, University of Alabama, Tuscaloosa, AL 35487
3 School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
Abstract. We review the results from recent parallel and other
deep HST surveys. Deep HST/WFPC2
images in U, B, V, I were analyzed using artificial neural
network (ANN) classifiers, which are
based on galaxy surface brightness and light profiles, and which
distinguish quite well between
E/S0's, Sabc's, and Sd/Irr for B
27 mag. We discuss
effects from the cosmological SB-dimming
and from the redshifted UV-morphology on the classifications, and
correct for the latter. The
median scale-length at B
≅ 27 mag is
rhl ≅
0".25-0".3 (1-2 kpc at z ≅
1-2). Early and
late-type galaxies are fairly well-separated in BVI
color-magnitude diagrams for B
27 mag, with
E/S0's being the reddest and Sd/Irr's generally blue. We present the
B-band galaxy counts
for ~ 36 WFPC2 fields as a function of morphological type for B
27 mag. E/S0's are only
marginally above the no-evolution predictions, and Sabc's are at most
0.5 dex above the non-evolving models for B
24 mag. The faint blue
galaxy counts in the B-band are dominated
by Sd/Irr's, and are explained by a combination of a moderately steep
local luminosity function
undergoing strong luminosity evolution plus low-luminosity
lower-redshift dwarf galaxies.
Deep WFPC2 images in the medium-band filter F410M
(Lyα at z
≅ 2.4) yielded 18 faint,
compact objects surrounding the radio galaxy 53W002 at z
≅ 2.390. These objects appear to
be star-forming spheroids smaller than the bulge of a spiral
galaxy. They are much smaller (rhl
≅ 0".1
≅ 0.5-1 kpc) and fainter
(MV (z = 0) = -21 -> -17) than typical galaxies
today, and
may the building blocks from which many of the luminous nearby galaxies
were formed through
repeated hierarchical mergers. Parallel F410M images of two other random
fields yielded 15
more z ≅ 2.4 candidates -
as faint and compact as the z
≅ 2.4 candidates in the 53W002
field - confirming that there may exist a widespread population of
compact, faint Lyα emitting galaxy
building blocks at z ≅
2.4, and presumably anywhere in the range z ~ 1-4. The
difference in the
number of objects from each F410M parallel field can be explained if
these subgalactic clumps exhibit some level of clustering at z
≅ 2.4 on Mpc scales, and
suggests that the group around
53W002 is no more than a ~
2
fluctuation in the density distribution. Deep KPNO 4m F410M
imaging and spectroscopy shows that the 53W002 cluster
stretches over 7'(~ 5 Mpc),
and may be part of some larger-scale structure at z
≅ 2.39.
Deep HST/PC images at ~ 0".06 FWHM resolution in BVI - as
well as in redshifted Lyα - of
the weak radio source 53W002 show several morphological components for
this compact narrow-line
galaxy at z = 2.390: (1) a blue point source (central AGN,
500 pc) with
20-25% of the
total continuum light; (2) a small, concentrated and somewhat redder
inner core; (3) an r1/4-like
light distribution with colors indicating an overall stellar population
age ~ 0.4 Gyr and no large
color or age gradient out to r ~ 9 kpc; and (4) two small blue clouds
roughly aligned with
the radio axis and the main stellar population, and separated by a red
linear feature, possibly a "dust" lane. The size and shape of the
Lyα clouds suggests reflected
AGN continuum-light shining through a cone (plus re-radiated
Lyα in emission). A recent
OVRO interferometric
CO-detection on both sides of 53W002 - and in the same direction
as the continuum clouds and
the radio jet - suggest a star-bursting region induced by the radio
jet. Hence, both mechanisms
likely play a role in explaining the "alignment effect." We discuss the
formation and evolution
scenario for 53W002 in context of its surrounding sub-galactic
objects.
Table of Contents
emitting
candidates at z ≅
2.4 emitting
z ≅ 2.4 candidates emitting
candidates at z ≅ 2.4 surveys
