The hosts of z=2z=2 QSOs

We present results of the hosts of four high-redshift ($z \approx 2$) 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 ($\sim$0.5$^\prime$$^\prime$) 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