511 research outputs found
The decade of galaxy formation: pitfalls in the path ahead
At the turn of the decade we arguably move from the era of precision
cosmology to the era of galaxy formation. One approach to this problem will be
via the construction of comprehensive galaxy samples. In this review I take the
opportunity to highlight a number of challenges which must be overcome before
we can use such data to construct a robust empirical blueprint of galaxy
evolution. The issues briefly highlighted here are: the Hubble tuning fork
versus galaxy components, the hierarchy of structure, the accuracy of
structural decompositions, galaxy photometry, incompleteness, cosmic variance,
photometric versus spectroscopic redshifts, wavelength bias, dust attenuation,
and the disconnect with theory. These concerns essentially form one of the key
motivations of the GAMA survey which, as one of its goals, will establish a
complete comprehensive kpc-resolution 3D multi-wavelength (UV-Opt-IR-Radio)
database of 250k galaxy systems to z <0.5.Comment: Review paper (12 pages, 11 figures) in "Hunting for the Dark: The
Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.Debattista
& C.C.Popescu, AIP Conf. Ser., in pres
The Ccontribution of normal, dim and dwarf galaxies to the local luminosity density
From the Hubble Deep Field catalog presented in Driver et al. (1998) we
derive the local (0.3 < z < 0.5) Bivariate Brightness Distribution (BBD) of
field galaxies within a 326 Mpc**3 Volume-Limited sample. The sample contains
47 galaxies which uniformally sample the underlying galaxy population within
the specified redshift, magnitude and surface brightness limits (0.3 < z < 0.5,
-21.3 < M_{B} < -13.7 mags, 18.0 < mu_{B} < 24.55 mags/sq arcsec). We conclude:
(i) A luminosity-surface brightness relation exists for both the field and
cluster galaxy populations, M_{B} ~ 1.5 mu_{e} - 50, (ii) Luminous low surface
brightness galaxies account for <10% of the L* population, (iii) Low luminosity
low surface brightness galaxies outnumber Hubble types by a factor of ~ 1.4,
however their space density is NOT sufficient to explain the faint blue excess
either by themselves or as faded remnants.
In terms of the local luminosity density and galaxy dynamical mass budget,
normal galaxies (i.e. Hubble tuning fork) contribute 88% and 72% respectively.
This compares to 7% and 12% for dim galaxies and 5% and 16% for dwarf galaxies
(within the above specified limits).Comment: Accepted for publication in Astrophysical Journal Letters. Nine pages
and two figure
Are disappearing dwarfs just lying low ?
Recent redshift surveys have shown that the excess galaxies seen in faint
galaxy number counts (above those expected given the local galaxy luminosity
function) are not evolved giants at high redshifts, but low to moderate
luminosity objects at more modest redshifts. This has led to the suggestion
that there was once an additional population of dwarf galaxies which has since
disappeared, ie. there is non-conservation of galaxy number. Here we
investigate the possibility that these disappearing dwarfs have actually
evolved to become the population of very low surface brightness galaxies which
is now being detected in nearby clusters.Comment: 12 pages, 7 figures. Figures available from
http://www.phys.unsw.edu.au/~spd/bib.htm
The local supermassive black hole mass density: corrections for dependencies on the Hubble constant
We have investigated past measurements of the local supermassive black hole
mass density, correcting for hitherto unknown dependencies on the Hubble
constant, which, in some cases, had led to an underestimation of the mass
density by factors of ~2. Correcting for this, we note that the majority of
past studies yield a local supermassive black hole mas density that is
consistent with the range 4.4-5.9 x 10^5 f(H_0) M_Sun / Mpc^3 (when using H_0 =
70 km/s/Mpc). In addition, we address a number of ways in which these past
estimates can be further developed. In particular, we tabulate realistic
bulge-to-total flux ratios which can be used to estimate the luminosity of
bulges and subsequently their central black hole masses.Comment: MNRAS, accepte
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