98 research outputs found
The hosts of QSOs
We present results of the hosts of four high-redshift () and
high luminosity (M_B \lsim -28 mag) QSOs, three radio-quiet one radio-loud,
imaged in R and K bands. The extensions to the nuclear unresolved source are
most likely due to the hosts galaxies of these QSOs, with luminosities at
rest-frame 2300\AA of at least 3-7% of the QSO luminosity, and most likely
around 6-18% of the QSO luminosity. Our observations show that, if the
extensions we have detected are indeed galaxies, extraordinary big and luminous
host galaxies are not only a characteristic of radio-loud objects, but of QSOs
as an entire class.Comment: 6 pages, 4 Figures, Latex, uses lamuphys.sty, also available at
http://www.mpa-garching.mpg.de/~itziar To appear in the Proceedings of the
ESO/IAC Conference on 'Quasar Hosts' ESO Astrophysics Symposia eds. D.
Clements and I. Perez-Fourno
V, R, I and Halpha photometry of circumnuclear star forming regions in four galaxies with different levels of nuclear activity
V,R,I continuum bands and Halpha + [NII] photometry for circumnuclear star
forming regions (CNSFR) is presented, for galaxies with different kinds of
nuclear activity: NGC 7469 (Sy 1), NGC 1068 (Sy 2), NGC 7177 (LINER) and NGC
3310 (Starburst). Their Halpha luminosities (0.02 - 7x10**40 erg/s; uncorrected
for internal extinction), are comparable to those observed in other galaxies.
No systematic differences in the broad band colours are found for the CNSFR in
the different galaxies, except for those in NGC 3310 which are considerably
bluer, partially due to a younger stellar population. Using theoretical
evolutionary synthesis models some colours can be reproduced by single
populations (between 7 and 300 Myr) and extinction 0.5-1.5 mag). However, in
many cases, the observed equivalent width of Halpha, require a younger
population. NGC 1068, 7177 and 7469, are fitted by a two-burst population model
at solar metallicity; the age difference between both populations is around 5-7
Myr and the younger burst involves 3 - 61% of the total mass of the
cluster,consistent with the younger burst being originated by supernova
activity from the previous one. NGC 3310, requires younger ionizing population
ages and lower metallicity. An excess (R-I) observed/predicted, not consistent
with a normal reddening law can be atributted to red supergiants present in the
older population, and not properly accounted for by the models. The
two-population scenario seems to show a trend of the evolutionary state of the
CNSFR with the nuclear type of the parent galaxy that remains to be explored.Comment: Accepted for publication in MNRAS, 22pages, 11 figure
Constraints on the Accuracy of Photometric Redshifts Derived from BLAST and Herschel/SPIRE Sub-mm Surveys
More than 150 galaxies have been detected in blank-field millimetre and
sub-millimetre surveys. However the redshift distribution of sub-mm galaxies
remains uncertain due to the difficulty in identifying their optical-IR
counterparts, and subsequently obtaining their spectroscopic emission-line
redshifts. In this paper we discuss results from a Monte-Carlo analysis of the
accuracy with which one can determine redshifts from photometric measurements
at sub-millimetre-FIR wavelengths. The analysis takes into account the
dispersion in colours introduced by including galaxies with a distribution of
SEDs, and by including photometric and absolute calibration errors associated
with real observations. We present examples of the probability distribution of
redshifts for individual galaxies detected in the future BLAST and
Herschel/SPIRE surveys. We show that the combination of BLAST and 850um
observations constrain the photometric redshifts with sufficient accuracy to
pursue a program of spectroscopic follow-up with the 100m GBT.Comment: 3 pages, 5 figures, in 2K1BC symposium "Experimental Cosmology at
Millimetre Wavelengths", ed. M. de Petris and M. Gervasi, AIP, in pres
Stellar populations in the nuclear regions of nearby radiogalaxies
We present optical spectra of the nuclei of seven luminous (P(178MHz) >
10**25 W Hz**(-1) Sr**(-1)) nearby (z<0.08) radiogalaxies, which mostly
correspond to the FR II class. In two cases, Hydra A and 3C 285, the Balmer and
4000A break indices constrain the spectral types and luminosity classes of the
stars involved, revealing that the blue spectra are dominated by blue
supergiant and/or giant stars. The ages derived for the last burst of star
formation in Hydra A are between 7 and 40 Myr, and in 3C 285 about 10 Myr. The
rest of the narrow-line radiogalaxies (four) have 4000A break and metallic
indices consistent with those of elliptical galaxies. The only broad-line
radiogalaxy in our sample, 3C 382, has a strong featureless blue continuum and
broad emission lines that dilute the underlying blue stellar spectra. We are
able to detect the Ca II triplet in absorption in the seven objects, with good
quality data for only four of them. The strengths of the absorptions are
similar to those found in normal elliptical galaxies, but these values are both
consistent with single stellar populations of ages as derived from the Balmer
absorption and break strengths, and, also, with mixed young+old populations.Comment: 14 pages, 16 figures, accepted by MNRA
Broad-band and Hα surface photometry of the central regions of nearby active galaxies - I. Observations
This is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society. Sánchez-Portal, M., Díaz, A.I., Terlevich, R., Terlevich, E., Álvarez Álvarez, M. and I. Aretxaga. Broad-band and Hα surface photometry of the central regions of nearby active galaxies - I. Observations. Monthly Notices of the Royal Astronomical Society 312 (2000): 2-3
Subaru Spectroscopy and Spectral Modeling of Cygnus A
We present high angular resolution (0.5) MIR spectra
of the powerful radio galaxy, Cygnus A, obtained with the Subaru telescope. The
overall shape of the spectra agree with previous high angular resolution MIR
observations, as well as previous Spitzer spectra. Our spectra, both on and off
nucleus, show a deep silicate absorption feature. The absorption feature can be
modeled with a blackbody obscured by cold dust or a clumpy torus. The deep
silicate feature is best fit by a simple model of a screened blackbody,
suggesting foreground absorption plays a significant, if not dominant role, in
shaping the spectrum of Cygnus A. This foreground absorption prevents a clear
view of the central engine and surrounding torus, making it difficult to
quantify the extent the torus attributes to the obscuration of the central
engine, but does not eliminate the need for a torus in Cygnus A
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