The Stellar Populations of Low-Luminosity Active Galactic Nuclei. II. Space Telescope Imaging Spectrograph Observations (original) (raw)
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Stellar Population In LLAGN. II: STIS Observations
Arxiv preprint astro-ph/ …, 2004
We present a study of the stellar population in Low Luminosity Active Galactic Nuclei (LLAGN). Our goal is to search for spectroscopic signatures of young and intermediate age stars, and to investigate their relationship with the ionization mechanism in LLAGN. The method used is based on the stellar population synthesis of the optical continuum of the innermost (20-100 pc) regions in these galaxies. For this purpose, we have collected high spatial resolution optical (2900-5700Å) STIS spectra of 28 nearby LLAGN that are available in the Hubble Space Telescope archive. The analysis of these data is compared with a similar analysis also presented here for 51 ground-based spectra of LLAGN. Our main findings 8 Jansky Fellow
The Stellar Populations of Low-Luminosity Active Galactic Nuclei. I. Ground-based Observations
Astrophysical Journal, 2004
In a recently completed survey of the stellar populations properties of LINERS and LINER/HII Transition Objects (TOs), we have identified a numerous class of galactic nuclei which stand out because of their conspicuous 10 8−9 yr populations, traced by high order Balmer absorption lines and other stellar indices. These objects were called "Young-TOs", since they all have TO-like emission line ratios. In this paper we extend this previous work, which concentrated on the nuclear properties, by investigating the radial variations of spectral properties in Low Luminosity Active Galactic Nuclei (LLAGN). Our analysis is based on high signal to noise long-slit spectra in the 3500-5500Å interval for a sample of 47 galaxies. The data probe distances of typically up to 850 pc from the nucleus with a resolution of ∼ 100 pc (∼ 1 ′′ ) and S/N ∼ 30. Stellar population gradients are mapped by the radial profiles of absorption line equivalent widths and continuum colours along the slit. These variations are further analyzed by means of a decomposition of each spectrum in terms of template galaxies representative of very young (≤ 10 7 yr), intermediate age (10 8−9 yr) and old (10 10 yr) stellar populations.
Monthly Notices of the Royal Astronomical Society, 2005
In a recently completed survey of the stellar populations properties of LINERS and LINER/HII Transition Objects (TOs), we have identified a numerous class of galactic nuclei which stand out because of their conspicuous 10 8−9 yr populations, traced by high order Balmer absorption lines and other stellar indices. These objects were called "Young-TOs", since they all have TO-like emission line ratios. In this paper we extend this previous work, which concentrated on the nuclear properties, by investigating the radial variations of spectral properties in Low Luminosity Active Galactic Nuclei (LLAGN). Our analysis is based on high signal to noise long-slit spectra in the 3500-5500Å interval for a sample of 47 galaxies. The data probe distances of typically up to 850 pc from the nucleus with a resolution of ∼ 100 pc (∼ 1 ′′ ) and S/N ∼ 30. Stellar population gradients are mapped by the radial profiles of absorption line equivalent widths and continuum colours along the slit. These variations are further analyzed by means of a decomposition of each spectrum in terms of template galaxies representative of very young (≤ 10 7 yr), intermediate age (10 8−9 yr) and old (10 10 yr) stellar populations.
Stellar Population in LLAGN. I: Ground-based observations
Arxiv preprint astro-ph/ …, 2004
We present a spectroscopic study of the stellar populations of Low Luminosity Active Galactic Nuclei (LLAGN). Our main goal is to determine whether the stars 10 Jansky Fellow 11 Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which are operated by AURA, Inc., under a cooperative agreement with the National Science Foundation.
An Optical Spectroscopic Atlas of Low‐Redshift Active Galactic Nuclei
The Astrophysical Journal Supplement Series, 2003
We present a spectral atlas of the H region for 215 type 1 AGNs (luminous Seyfert 1/radio galaxy nuclei and low-z quasars) up to z % 0:8. Line profiles and measures were derived from the database of intermediate resolution spectra (Re1000) with average continuum level S/N ratio %30. Parameters including rest frame equivalent width and FWHM are provided for the Fe ii opt blend at 4570, H, He ii 4686, and the [O iii] 4959, 5007 emission lines. We extract clean broad component H profiles and provide wavelength measurements at 0, 1/4, 1/2, 3/4, and 0.9 peak intensity levels in order to permit a quantitative definition of the H broad component for statistical studies. We also discuss sources of uncertainty, selection effects, and biases in our sample. The data are especially important for tests of the eigenvector 1 parameter space occupation and correlation. We show that the I Zw 1 template Fe ii opt spectrum reproduces well the observed Fe ii opt emission for a wide range of line width and strength. A detailed analysis of the data within the eigenvector 1 context is deferred to a companion paper. E 199 2. OBSERVATIONS Spectra were obtained with very similar instrumental setups yielding resolution in the range 4-7.5 Å FWHM. The median value of the S/N of our spectra is %25. shows the distribution of S/N values for our sample. We use the value for an average spectrum in the case of sources with multiple spectra of comparable quality. Spectra were obtained with the following telescopes and spectrographs: ESO 1.5 m (B&Ch), San Pedro Martir 2.2 m (B&Ch), Calar Alto 2.2 m (B&Ch), KPNO 2.2 m (Gold), and Asiago 1.82 m (B&Ch). Results based on analysis of parts of this sample can be found in
THE PRESENCE OF WEAK ACTIVE GALACTIC NUCLEI IN HIGH REDSHIFT STAR-FORMING GALAXIES
Astrophysical Journal, 2010
We present [OIII 5007A] observations of the star forming galaxy HDF-BMZ1299 (z=1.598) using Keck Observatory's Adaptive Optics system with the near-infrared integral field spectrograph OSIRIS. Using previous Halpha and [NII] measurements of the same source, we are able for the first time to use spatially resolved observations to place a high-redshift galaxy's substructure on a traditional HII diagnostic diagram. We find that HDF-BMZ1299's spatially concentrated nebular ratios in the central ~1.5 kiloparsec (0."2) are best explained by the presence of an AGN: log([NII]/Halpha)=-0.22+/-0.05 and 2sigma limit of log([OIII]/Hbeta)>0.26. The dominant energy source of this galaxy is star formation, and integrating a single aperture across the galaxy yields nebular ratios that are composite spectra from both AGN and HII regions. The presence of an embedded AGN in HDF-BMZ1299 may suggest a potential contamination in a fraction of other high-redshift star forming galaxies, and we suggest that this may be a source of the "elevated" nebular ratios previously seen in seeing-limited metallicity studies. HDF-BMZ1299's estimated AGN luminosity is L_Halpha = 3.7e41 erg/s and L_[OIII] = 5.8e41 erg/s, making it one of the lowest luminosity AGN discovered at this early epoch.
Astronomical Journal, 2008
In several studies of Low Luminosity Active Galactic Nuclei (LLAGNs), we have characterized the properties of the stellar populations in LINERs and LINER/HII Transition Objects (TOs). We have found a numerous class of galactic nuclei which stand out because of their conspicuous 0.1-1 Gyr populations. These nuclei were called "Young-TOs" since they all have TO-like emission line ratios. To advance our knowledge of the nature of the central source in LLAGNs and its relation with stellar clusters, we are carrying out several imaging projects with the Hubble Space Telescope (HST) at near-UV, optical and near-IR wavelengths. In this paper, we present the first results obtained with observations of the central regions of 57 LLAGNs imaged with the WFPC2 through any of the V (F555W, F547M, F614W) and I (F791W, F814W) filters that are available in the HST archive. The sample contains 34% of the LINERs and 36% of the TOs in the Palomar sample. The mean spatial resolution of these images is 10 pc. With these data we have built an atlas that includes structural maps for all the galaxies, useful to identify compact nuclear sources and, additionally, to characterize the circumnuclear environment of LLAGNs, determining the frequency of dust and its morphology. The main results obtained are: 1) We have not found any correlation between the presence of nuclear compact sources and emission-line type. Thus, nucleated LINERs are as frequent as nucleated TOs. 2) The nuclei of "Young-TOs" are brighter than the nuclei of "Old-TOs" and LINERs. These results confirm our previous results that Young-TOs are separated from other LLAGNs classes in terms of their central stellar population properties and brightness. 3) Circumnuclear dust is detected in 88% of the LLAGNs, being almost ubiquitous in TOs. 4) The dust morphology is complex and varied, from nuclear spiral lanes to chaotic filaments and nuclear disk-like structures. Chaotic filaments are as frequent as dust spirals; but nuclear disks are mainly seen in LINERs. These results suggest an evolutionary sequence of the dust in LLAGNs, LINERs being the more evolved systems and Young-TOs the youngest.
The Astrophysical Journal, 1999
This study explores the space density and properties of active galaxies to z≃0.8. We have investigated the frequency and nature of unresolved nuclei in galaxies at moderate redshift as indicators of nuclear activity such as Active Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged galaxies with multi-component models using maximum likelihood estimate techniques to determine the best model fit. We select those galaxies requiring an unresolved point-source component in the galaxy nucleus, in addition to a disk and/or bulge component, to adequately model the galaxy light. We have searched 70 WFPC2 images primarily from the Medium Deep Survey for galaxies containing compact nuclei. In our survey of 1033 galaxies, the fraction containing an unresolved nuclear component ≥5% of the total galaxy light is 9±1% corrected for incompleteness. In this second of two papers in this series, we discuss the nature of the compact nuclei and their hosts. We present the upper limit luminosity function (LF) for low-luminosity AGN (LLAGN) in two redshift bins to z=0.8. Mild number density evolution is detected of the form φ∝(1+z) 1.9 for nuclei at-18 ∼ <M B ∼ <-14. The LFs appear to flatten at M B ≥-16 and this flatness, combined with the increase in number density, is inconsistent with pure luminosity evolution. Based on the amount of density evolution observed for these objects, we find that almost all present-day spiral galaxies could have hosted a LLAGN at some point in their lives. We also comment on the likely contribution of these compact nuclei to the soft X-ray background.
Monthly Notices of the Royal Astronomical Society, 2000
We present photometry, in V,R,I continuum bands and in the Hα + [NII] emission lines, for a sample of four circumnuclear star forming regions (CNSFR), located in galaxies with different kinds of activity in their nuclei: NGC 7469 (Sy 1), NGC 1068 (Sy 2), NGC 7177 (LINER) and NGC 3310 (Starburst).
Nearby early-type galaxies with ionized gas. Characterization of the underlying stellar population
2005
We present a preliminary analysis of the sample of early type galaxies of , selected to build a data-set of spectral properties of well studied early-type galaxies showing emission lines. Because of the presence of emission lines, the sample is biased toward objects that might be expected to have ongoing and recent star formation. We have compared the linestrength indices presented in with Simple Stellar Populations (SSPs) in order to characterize the underlying stellar population of the galaxies. We have derived ages, metallicities and [α/Fe] ratios. The positive trend of the σ-metallicity and σ − [α/Fe] relations is reproduced. The bulk of the galaxies span a range in metallicity from ∼ solar to ∼ twice solar and a range in [α/Fe] from ∼ 0.2 to ∼ 0.4. Furthermore the comparison of the derived parameters at different galactocentric distances shows the presence of negative metallicity gradients from the center outwards.