Refine
Has Fulltext
- no (10)
Year of publication
- 2004 (10) (remove)
Document Type
- Article (10)
Language
- English (10)
Is part of the Bibliography
- yes (10)
Institute
This paper presents observations of an extended Lyman-alpha emission nebula surrounding the galaxy responsible for the Damped Lyman-alpha Absorption (DLA) line in the spectrum of the quasar Q2233+131. With the Potsdam Multi Aperture Spectrophotometer (PMAS) we measure the properties of the extended Lyalpha emission in an area of 3" x 5" having a total line flux of (2.8 +/- 0.3) x 10(-16) erg cm(-2) s(-1), which at redshift z = 3.15 corresponds to a luminosity of (2.4(-0.2)(+0.3)) x 10(43) erg s(-1) and a size of 23 x 38 kpc. The location of the emission is spatially coincident with the previously detected DLA galaxy, but extends significantly beyond its limb. We argue that the Lya emission is likely to be caused by an outflow from the DLA galaxy, presumably powered by star formation. In the case of negligible dust extinction, the Lya luminosity indicates a star-formation rate of 19 +/- 10 M-. yr(-1) consistent with that derived from the UV continuum flux from the parent galaxy. The wind velocity indicated by the integral field spectra is of the order of several hundred km s(-1). We find no indication of emission originating in a rotating disk
We present spatially resolved spectrophotometric observations of multiply imaged QSOs, using the Potsdam Multi- Aperture Spectrophotometer (PMAS), with the intention to search for spectral differences between components indicative of either microlensing or dust extinction. For the quadruple QSO HE 0435-1223 we find that the continuum shapes are indistinguishable, therefore differential extinction is negligible. The equivalent widths of the broad emission lines are however significantly different, and we argue that this is most likely due to microlensing. Contrariwise, the two components of the well-known object UM 673 have virtually identical emission line properties, but the continuum slopes differ significantly and indicate different dust extinction along both lines of sight
We report preliminary results from a targeted investigation on quasars containing damped Lyman-alpha absorption (DLA) lines as well strong metal absorption lines, carried out with the Potsdam Multi Aperture Spectrophotometer (PMAS). We search for line-emitting objects at the same redshift as the absorption lines and close to the line of sight of the QSOs. We have observed and detected the already confirmed absorbing galaxies in Q2233+131 (Z(abs) = 3.15) and Q0151+045 (Z(abs),= 0.168), while failing to find spectral signatures for the z = 0.091 absorber in Q0738+313. From the Q2233+131 DLA galaxy, we have detected extended Lyalpha emission from an area of 3" x 5"
We describe a project to study the state of the ISM in similar to20 low redshift (z < 0.3) QSO host galaxies observed with the PMAS integral field spectrograph. We describe the development of the method to access the stellar and gas components of the spectrum without the strong nuclear emission, in order to access the host galaxy properties in the central region. It shows that integral field spectroscopy promises to be very efficient in studying the gas distribution and its velocity field, and also the spatially resolved stellar population in the host galaxies of luminous AGN
We investigate multicolour imaging data of a complete sample of 19 low-redshift (z < 0.2) quasar host galaxies. The sample was imaged in four optical (BVRi) and three near-infrared bands (JHK(s)). Galaxy types, structural parameters and robust host galaxy luminosities are extracted for all bands by means of two-dimensional deblending of galaxy and nucleus. For the disc-dominated fraction of host galaxies (Sa and later) the optical and optical-to-near-infrared colours agree well with the average colours of inactive galaxies of the same type. The bulge-dominated galaxies (E/S0), on the other hand, appear a significant 0.3 mag bluer in (V-K) than their inactive counterparts, being as blue as the discs in the sample. This trend is confirmed by fitting population synthesis models to the extracted broad-band spectral energy distributions: the stellar population age of the bulge-dominated hosts lies around a few Gyr, much younger than expected for old evolved ellipticals. Comparison to other studies suggests a strong trend for stellar age in elliptical host galaxies with luminosity. Intermediately luminous elliptical hosts have comparably young populations, either intrinsically or from an enhanced star formation rate potentially due to interaction; the most luminous and massive ellipticals on the contrary show old populations. The correspondence between the nuclear activity and the blue colours suggests a connection between galaxy interaction, induced star formation and the triggering of nuclear activity. However, the existence of very symmetric and undisturbed discs and elliptical host galaxies emphasized that other mechanisms like minor merging or gas accretion must exist
We have performed Hubble Space Telescope imaging of a sample of 23 high-redshift (1.8<z<2.75) active galactic nuclei (AGNs), drawn from the COMBO-17 survey. The sample contains moderately luminous quasars (M(B)similar to-23). The data are part of the Galaxy Evolution from Morphologies and SEDs imaging survey that provides high-resolution optical images obtained with the Advanced Camera for Surveys in two bands (F606W and F850LP), sampling the rest-frame UV flux of the targets. To deblend the AGN images into nuclear and resolved (host galaxy) components, we use a point-spread function subtraction technique that is strictly conservative with respect to the flux of the host galaxy. We resolve the host galaxies in both filter bands in nine of the 23 AGNs, whereas the remaining 14 objects are considered nondetections, with upper limits of less than 5% of the nuclear flux. However, when we co-add the unresolved AGN images into a single high signal-to-noise ratio composite image, we find again an unambiguously resolved host galaxy. The recovered host galaxies have apparent magnitudes of 23.0<F606W<26.0 and 22.5<F850LP<24.5, with rest-frame UV colors in the range -0.2<(F606W-F850LP)(obs)<2.3. The rest-frame absolute magnitudes at 200 nm are -20.0<M-200 nm<-22.2. The photometric properties of the composite host are consistent with the individual resolved host galaxies. We find that the UV colors of all host galaxies are substantially bluer than expected from an old population of stars with formation redshift z<=5, independent of the assumed metallicities. These UV colors and luminosities range up to the values found for Lyman break galaxies (LBGs) at z=3. Our results suggest either a recent starburst of, e. g., a few percent of the total stellar mass at 100 Myr before observation, with mass fraction and age strongly degenerate, or the possibility that the detected UV emission may be due to young stars forming continuously. For the latter case we estimate star formation rates of typically &SIM;6 M&ODOT; yr(-1) (uncorrected for internal dust attenuation), which again lies in the range of rates implied from the UV flux of LBGs. Our results agree with the recent discovery of enhanced blue stellar light in AGN hosts at lower redshifts
VLT on-axis optical spectroscopy of the z = 0.144 radio-loud quasar HE 1434-1600 is presented. The spatially resolved spectra of the host galaxy are deconvolved and separated from those of the central quasar in order to study the dynamics of the stars and gas as well as the physical conditions of the ISM. We find that the host of HE 1434-1600 is an elliptical galaxy that resides in a group of at least 5 member galaxies, and that most likely experienced a recent collision with its nearest companion. Compared with other quasar host galaxies, HE 1434-1600 has a highly ionized ISM. The ionization state corresponds to that of typical Seyferts, but the ionized regions are not distributed in a homogeneous way around the QSO, and are located preferentially several kiloparsecs away from it. While the stellar absorption lines do not show any significant velocity field, the gas emission lines do. The observed gas velocity field is hard to reconcile with dynamical models involving rotating disk. modified Hubble laws or power laws, that all require extreme central masses (M > 10(9) M-circle dot) to provide only poor fit to the data. Power law models, which best fit the data, provide a total mass of M(<10 kpc) = 9.2 x 10(10) M-&ODOT;. We conclude that the recent interaction between HE 1434-1600 and its closest companion has strongly affected the gas velocity and ionization state, from the center of the galaxy to its most external parts
We describe an algorithm to decompose deep images of active galactic nuclei into host galaxy and nuclear components. Currently supported are three galaxy models: a de Vaucouleurs spheroidal; an exponential disc; and a two- component disc + bulge model. Key features of the method are: (semi-)analytic representation of a possibly spatially variable point spread function; full two-dimensional convolution of the model galaxy using gradient-controlled adaptive subpixelling; and a multiple iteration scheme. The code is computationally efficient and versatile for a wide range of applications. The quantitative performance is measured by analysing simulated imaging data. We also present examples of the application of the method to small test samples of nearby Seyfert 1 galaxies and quasars at redshifts z < 0.35
We present the results from a study of the host galaxies of 15 optically selected active galactic nuclei (AGNs) with 0.5<z<1.1 from the Galaxy Evolution from Morphology and SEDs project (GEMS). GEMS is a Hubble Space Telescope imaging survey of a similar to28' x 28' contiguous field centered on the Chandra Deep Field-South in the F606W and F850LP filter bands. It incorporates the spectral energy distributions and redshifts of similar to10,000 objects, obtained by the COMBO-17 project. We have detected the host galaxies of all 15 AGNs in the F850LP band (and 13 of 15 in the F606W band), recovering their fluxes, morphologies, and structural parameters. We find that 80% of the host galaxies have early-type (bulge-dominated) morphologies, while the rest have structures characteristic of late-type (disk-dominated) galaxies. We find that 25% of the early types and 30% of the late types exhibit disturbances consistent with galaxy interactions. The hosts show a wide range of colors, from those of red-sequence galaxies to blue colors consistent with ongoing star formation. Roughly 70% of the morphologically early-type hosts have rest-frame blue colors, a much larger fraction than those typical of nonactive morphologically early-type galaxies in this redshift and luminosity range. Yet, we find that the early-type hosts are structurally similar to red-sequence elliptical galaxies, inasmuch as they follow an absolute magnitude versus half-light size correlation that is consistent with the mean relation for early-type galaxies at similar redshifts
The quasar HE 0047-1756, at z = 1.67, is found to be split into two images 1."144 apart by an intervening galaxy acting as a gravitational lens. The flux ratio for the two components is roughly 3.5:1, depending slightly upon wavelength. The lensing galaxy is seen on images obtained in the i (800 nm) and K-s bands (2.1 mum); there is also a nearby faint object which may be responsible for some shear. The spectra of the two quasar images are nearly identical, but the emission line ratio between the two components scale differently from the continuum. Moreover, the fainter component has a bluer continuum slope than the brighter one. We argue that these small differences are probably due to microlensing. There is evidence for a partial Einstein ring emanating from the brighter image toward the fainter one