TY - JOUR
T1 - Star formation in luminous quasar host galaxies at z=1-2
AU - Floyd, David J. E.
AU - Dunlop, James S.
AU - Kukula, Marek J.
AU - Brown, Michael J. I.
AU - McLure, Ross J.
AU - Baum, Stefi A.
AU - O'Dea, Christopher P.
PY - 2012/8/1
Y1 - 2012/8/1
N2 - We present deep HST/WFPC2, rest-frame U images of 17 ~L* quasars at z~1
and z~2 (V and I bands respectively), designed to explore the host
galaxies. We fit the images with simple axisymmetric galaxy models,
including a point-source in order to separate nuclear and host-galaxy
emission. We successfully model all of the host galaxies, with
luminosities stable to within 0.3 mag. Combining with our earlier NICMOS
rest-frame optical study of the same sample, we provide the first
rest-frame U-V colours for a sample of quasar host galaxies. While the
optical luminosities of their host galaxies indicate that they are drawn
purely from the most massive (>~L*) early-type galaxy population,
their colours are systematically bluer than those of comparably massive
galaxies at the same redshift. The host galaxies of the radio-loud
quasars (RLQ) in our sample are more luminous than their radio-quiet
quasar (RQQ) counterparts at each epoch, but have indistinguishable
colours, confirming that the RLQ's are drawn from only the most massive
galaxies (10^{11}-10^{12} M_sun even at z~2), while the RQQ's are
slightly less massive (~10^{11} M_sun). Using simple stellar population
"frosting" models we estimate that ~1% of the mass of the host galaxies
is undergoing star formation at z~2 and ~0.1% at z~1. The mean star
formation rates are ~350 M_sun/yr for the RLQ's and ~100 M_sun/yr for
the RQQ's at z~2. By z~1, these rates have fallen to ~150 M_sun/yr for
the RLQ's and ~50 M_sun/yr for the RQQ's. We conclude that while the
host galaxies are extremely massive, they remain actively star-forming
at, or close to, the epoch of the quasar.
AB - We present deep HST/WFPC2, rest-frame U images of 17 ~L* quasars at z~1
and z~2 (V and I bands respectively), designed to explore the host
galaxies. We fit the images with simple axisymmetric galaxy models,
including a point-source in order to separate nuclear and host-galaxy
emission. We successfully model all of the host galaxies, with
luminosities stable to within 0.3 mag. Combining with our earlier NICMOS
rest-frame optical study of the same sample, we provide the first
rest-frame U-V colours for a sample of quasar host galaxies. While the
optical luminosities of their host galaxies indicate that they are drawn
purely from the most massive (>~L*) early-type galaxy population,
their colours are systematically bluer than those of comparably massive
galaxies at the same redshift. The host galaxies of the radio-loud
quasars (RLQ) in our sample are more luminous than their radio-quiet
quasar (RQQ) counterparts at each epoch, but have indistinguishable
colours, confirming that the RLQ's are drawn from only the most massive
galaxies (10^{11}-10^{12} M_sun even at z~2), while the RQQ's are
slightly less massive (~10^{11} M_sun). Using simple stellar population
"frosting" models we estimate that ~1% of the mass of the host galaxies
is undergoing star formation at z~2 and ~0.1% at z~1. The mean star
formation rates are ~350 M_sun/yr for the RLQ's and ~100 M_sun/yr for
the RQQ's at z~2. By z~1, these rates have fallen to ~150 M_sun/yr for
the RLQ's and ~50 M_sun/yr for the RQQ's. We conclude that while the
host galaxies are extremely massive, they remain actively star-forming
at, or close to, the epoch of the quasar.
U2 - 10.1093/mnras/sts291
DO - 10.1093/mnras/sts291
M3 - Article
SN - 0035-8711
VL - 429
SP - 2
EP - 19
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 1
ER -