Ultraviolet‐Optical Observations of the Seyfert 2 Galaxies NGC 7130, NGC 5135, and IC 3639: Implications for the Starburst–Active Galactic Nucleus Connection (original) (raw)
Publications of the Astronomical Society of Japan, 2010
We present near-infrared K-(1.9-2.5µm) and L-(2.8-4.2µm) band spectroscopy of 22 Seyfert nuclei. We use two methods to investigate the presence of nuclear starbursts: (1) the Polycyclic Aromatic Hydrocarbon (PAH) emission feature at λ rest = 3.3 µm in the rest frame of L-band spectrum (a starburst indicator) and (2) the CO absorption feature at λ rest = 2.3-2.4 µm in the rest frame of the K-band spectrum, originating in the CO molecule. We clearly detected the 3.3 µm PAH emission features in five objects and the CO absorption features in 17 objects. Seyfert 2 galaxies tend to show bluer K − L colors compared with Seyfert 1 galaxies. We interpret the discrepancy as resulting from relative strength of stellar emission because AGN emission is affected by dust extinction. The 3.3 µm PAH emission luminosity (L 3.3P AH ) distributions for the Seyfert 1s and Seyfert 2s are very similar when normalized to the AGN power. Star-formation rates estimated from L 3.3P AH could be large enough to inflate the dusty torus by supernova explosion. We find that L 3.3P AH positively correlates with N-band luminosity with small aperture over a wide AGN luminosity range, and is independent of physical area we probed. The results suggest that nuclear region has a concentration of star formation and the star formation would control AGN activity.
Seyfert 2 galaxies in the GeV band: jets and starburst
2010
Context. The Fermi/LAT collaboration recently reported the detection of starburt galaxies in the high energy γ-ray domain, as well as radio-loud narrow-line Seyfert 1 objects. Aims. Motivated by the presence of sources close to the location of composite starburst/Seyfert 2 galaxies in the first year Fermi/LAT catalogue, we aim at studying high energy γ-ray emission from such objects, and at disentangling the emission of starburst and Seyfert activity. Methods. We analysed 1.6 years of Fermi/LAT data from NGC 1068 and NGC 4945, which count among the brightest Seyfert 2 galaxies. We search for potential variability of the high energy signal, and derive a spectrum of these sources. We also analyse public INTEGRAL IBIS/ISGRI data over the last seven years to derive their hard X-ray spectrum. Results. We find an excess of high energy γ-rays of 8.3 σ and 9.2 σ for 1FGL J0242.7+0007 and 1FGL J1305.4−4928, which are found to be consistent with the position of the Seyfert 2 galaxies NGC 1068 and NGC 4945, respectively. The energy spectrum of the sources can be described by a power law with a photon index of Γ = 2.31 ± 0.13 and a flux of F 100 MeV−100 GeV =(8.60 ± 2.27) × 10 −12 erg cm −2 s −1 for NGC 1068, while for NGC 4945, we obtain a photon index of Γ = 2.31 ± 0.10 and a flux of F 100 MeV−100 GeV =(1.58 ± 0.32) × 10 −11 erg cm −2 s −1 . For both sources, we detect no significant variability nor any indication of a curvature of the spectrum. While the high energy emission of NGC 4945 is consistent with starburst activity, that of NGC 1068 is an order of magnitude above expectations, suggesting dominant emission from the active nucleus. We show that a leptonic scenario can account for the multi-wavelength spectral energy distribution of NGC 1068. Conclusions. High energy γ-ray emission is revealed for the first time in a Seyfert 2 galaxy. If this result is confirmed in other objects, new perspectives would be opened up into the GeV band, with the discovery of a new class of high energy γ-ray emitters.
Publ Astron Soc Jpn, 2010
We present near-infrared K- (1.9-2.5μm) and L- (2.8-4.2μm) band spectroscopy of 22 Seyfert nuclei. We used two methods to investigate the presence of nuclear starbursts: (1) the Polycyclic Aromatic Hydrocarbon (PAH) emission feature at λrest = 3.3μm in the rest frame of the K-band spectrum (a starburst indicator) and (2) the CO absorption feature at λrest = 2.3-2.4μm in the rest frame of the K-band spectrum, originating in the CO molecule. We clearly detected the 3.3μm PAH emission features in five objects and the CO absorption features in 17 objects. Seyfert 2 galaxies tend to show bluer K - L colors compared with Seyfert 1 galaxies. We interpret the discrepancy as resulting from the relative strength of stellar emission because AGN emission is affected by dust extinction. The 3.3μm PAH emission luminosity (L3.3PAH) distributions for the Seyfert 1s and Seyfert 2s are very similar when normalized to the AGN power. The star-formation rates estimated from L3.3PAH could be large enough to inflate the dusty torus by a supernova explosion. We find that L3.3PAH positively correlates with the N-band luminosity with small aperture over a wide AGN luminosity range, and is independent of the physical area we probed. The results suggest that the nuclear region has a concentration of star formation and it would control the AGN activity.
The Astrophysical Journal Supplement Series, 2009
We have analyzed FUSE (905-1187Å) spectra of a sample of 16 local starburst galaxies. These galaxies cover almost three orders of magnitude in starformation rates and over two orders of magnitude in stellar mass. Absorption features from the stars and interstellar medium are observed in all the spectra. The strongest interstellar absorption features are generally blue-shifted by ∼ 50 to 300 km s −1 , implying the almost ubiquitous presence of starburst-driven galactic winds in this sample. The outflow velocites increase with both the star formation rate and the star formation rate per unit stellar mass, consistent with a galactic wind driven by the population of massive stars. We find outflowing coronal-phase gas (T ∼ 10 5.5 K) detected via the O VI absorption-line in nearly every galaxy. The O VI absorption-line profile is optically-thin, is generally weak near the galaxy systemic velocity, and has a higher mean outflow velocity than seen in the lower ionization lines. The relationship between the line width and column density for the O VI absorbing gas is in good agreement with expectations for radiatively cooling and outflowing gas. Such gas will be created in the interaction of the hot out-rushing wind seen in X-ray emission and cool dense ambient material. O VI emission is not generally detected in our sample, suggesting that radiative cooling by the coronal gas is not dynamically significant in draining energy from galactic winds. We find that the measured outflow velocities in the HI and HII phases of the interstellar gas in a given galaxy increase with the strength (equivalent width) of the absorption feature and not with the a FUV luminosity derived from FUSE LiF 2A continuum flux at 1150Å. Values are corrected for MW extinction using the method of and the E(B-V) values given in this table.
Near-infrared line imaging of the starburst galaxies NGC 520, NGC 1614 and NGC 7714
Astronomy and Astrophysics, 2001
We present high spatial resolution (∼0. ′′ 6) near-infrared broad-band JHK images and Brγ 2.1661 µm and H 2 1-0 S(1) 2.122 µm emission line images of the nuclear regions in the interacting starburst galaxies NGC 520, NGC 1614 and NGC 7714. The near-infrared emission line and radio morphologies are in general agreement, although there are differences in details. In NGC 1614, we detect a nuclear double structure in Brγ, in agreement with the radio double structure. We derive average extinctions of A K = 0.41 and A K = 0.18 toward the nuclear regions of NGC 1614 and NGC 7714, respectively. For NGC 520, the extinction is much higher, A K = 1.2 -1.6. The observed H 2 /Brγ ratios indicate that the main excitation mechanism of the molecular gas is fluorescence by intense UV radiation from clusters of hot young stars, while shock excitation can be ruled out.
Compact starburst in the central regions of Seyfert galaxies
We have conducted a high-resolution "3D" imaging survey of the CO(1-0), HCN(1-0), and HCO + (1-0) lines toward the central a few kpc regions of the Seyfert and starburst galaxies in the local universe using the Nobeyama Millimeter Array. We detected luminous HCN(1-0) emissions toward a considerable fraction of these Seyfert galaxies (10 of 12 in our sub-sample), which indicated that some of these Seyfert galaxies, such as NGC 3079, NGC 3227, NGC 4051, NGC 6764, and NGC 7479, are indeed accompanied with compact nuclear starburst, given the tight correlation between the HCN(1-0) luminosity and the star formation rate among star-forming galaxies. However, we suggest that the elevated HCN(1-0) emission from some of these Seyfert galaxies, including NGC 1068, NGC 1097, NGC 5033, and NGC 5194, does not signify the presence of massive starbursts there. This is because these Seyfert nuclei show abnormally high HCN(1-0)/HCO + (1-0) ratios (2-3), which were never observed in the starburst nuclei in our sample. This could be attributed to the overabundance of HCN molecules in the X-ray dominated regions (XDRs) at the centers of these Seyfert galaxies.
Probing nuclear starburst activity in a sample of nearby spiral galaxies
Astronomy and Astrophysics
As part of a systematic study of the UV properties of galaxies in the IUE library, we present in this paper an analysis of nuclear stellar populations in spiral galaxies with radial velocity ≤ 5 000 km s −1 . In this sample of 60 galaxies the IUE aperture probes a mean 1.0 kpc × 2.1 kpc area. Prior to any comparison of galaxy spectra in the range covered by IUE (1200-3200Å), we have formed subsets according to the absolute magnitude and morphological type of the studied galaxies. In a second step, and within each subset, we have co-added the spectra, and hence the objects into groups of similar spectral properties in the UV, also taking into account their spectral properties in the visible/nearinfrared ranges. As a result, high signal-to-noise ratio templates have been obtained, and information on spectral features can now be extracted and interpreted. We distinguish 4 groups for Sa, 8 for Sb, and 4 for Sc galaxies. We have carried out population syntheses using as base elements: H ii regions, integrated star clusters, and far-UV weak elliptical galaxies as representative of bulge stellar population. The variety of UV spectral types found in the central regions of spiral galaxies can be readily explained by different mixtures of bulge, circumnuclear burst and disc populations. Across different morphological types, similar templates can also be found. This is due to compensation effects of bulge contribution with the disc and circumnuclear burst ones. Flux fractions derived from the population synthesis have been converted into mass contributions and inferences have been made on the star-formation histories. In the central kpc of the galaxies with strong UV flux, we find that the mass stored in the young components (t < 500 Myr) is typically ≈ 10 7 M . We confirm that such star-formation enhancements occur preferentially in barred spirals. Internal reddening in the templates has been studied and inferences have been made on the corresponding reddening laws. We find cases where an SMC-like law applies and others where a faint λ2200Å absorption feature occurs resembling the reddening law of the LMC. The interest of the IUE data set resides in its rather large entrance aperture which samples a large portion of nearby galaxies, and is therefore quite suitable for the interpretation of large redshift galaxies.
The Astronomical Journal, 2011
We present 46 rest-frame ultraviolet (UV) spectra of 28 local starburst and star-forming galaxies which were observed with the Faint Object Spectrograph (FOS) and the Goddard High Resolution Spectrograph (GHRS) of the Hubble Space Telescope (HST) at a spectral resolution of a few 100 km s 1. We compare the HST spectra with lower resolution International Ultraviolet Explorer (IUE) spectra of the same galaxies and find systematic differences: the bright star clusters targeted in HST's ~1 apertures provide about 15% of the starburst luminosity traced by IUE's 10 20 aperture; they are bluer and have stronger stellar-wind features suggesting that the HST apertures have preferentially been placed on the youngest areas of the burst. In contrast, lines arising from the interstellar medium (ISM) show similar equivalent widths in both the large and small aperture observations, suggesting similar ISM properties from larger to smaller scales. In order to quantify the UV spectral morphology of star-forming galaxies, we created a set of UV line indices similar to the standard optical Lick indices. We discuss the relation between the UV spectral morphology and the properties of the galaxy host. We present our atlas of FOS and GHRS spectra both in print and electronically. The data set is useful as a baseline for comparisons with observations of the rest-frame UV spectra of star-forming galaxies at high redshift.
AGN and starburst in bright Seyfert galaxies: from IR photometry to IR spectroscopy
Arxiv preprint arXiv:0901.1212, 2009
Favor de proporcionar un resumen en español. If you are unable to translate your abstract into Spanish, the editors will do it for you. Infrared photometry and later infrared spectroscopy provided powerful diagnostics to distinguish between the main emission mechanisms in galaxies: AGN and Starburst. After the pioneering work on infrared photometry with IRAS in the far-IR and the S.Pedro Martir and ESO ground-based work in the near-IR, ISO photometry extended up to 200µm the coverage of the galaxies energy distributions. Then Spitzer collected accurate mid-infrared spectroscopy on different samples of galaxies. We will review the work done on the 12µm galaxy sample since the times of IRAS photometry to the new Spitzer spectroscopy. The main results on the multifrequency data of 12µm selected Seyfert galaxies are presented and discussed in the light of unification and evolution models. The spectroscopic work of Spitzer will soon be complemented at longer wavelengths by the Herschel spectrometers and in the future by SPICA at higher redshift.
The Far‐Infrared Emission Line and Continuum Spectrum of the Seyfert Galaxy NGC 1068
The Astrophysical Journal, 2005
We report on the analysis of the first complete far-infrared spectrum (43-197µm) of the Seyfert 2 galaxy NGC 1068 as observed with the Long Wavelength Spectrometer (LWS) onboard the Infrared Space Observatory (ISO). In addition to the 7 expected ionic fine structure emission lines, the OH rotational lines at 79, 119 and 163µm were all detected in emission, which is unique among galaxies with full LWS spectra, where the 119µm line, when detected, is always in absorption. The observed line intensities were modelled together with ISO Short Wavelength Spectrometer (SWS) and optical and ultraviolet line intensities from the literature, considering two independent emission components: the AGN component and the starburst component in the circumnuclear ring of ∼ 3 kpc in size. Using the UV to mid-IR emission line spectrum to constrain the nuclear ionizing continuum, we have confirmed previous results: a canonical power-law ionizing spectrum is a poorer fit than one with a deep absorption trough, while the presence of a big blue bump is ruled out. Based on the instantaneous starburst age of 5 Myr constrained by the Br γ equivalent width in the starburst ring, and starburst synthesis models of the mid-and far-infrared fine-structure line emission, a low ionization parameter (U=10 −3.5) and low densities (n=100 cm −3) are derived. Combining the AGN and starburst components, we succeeded in modeling the overall UV to far-IR atomic spectrum of NGC 1068, reproducing the line fluxes to within a factor 2.0 on average with a standard deviation of 1.3, and the overall continuum as the sum of the contribution of the thermal dust emission in the ionized and neutral components. The OH 119 µm emission indicates that the line is collisionally excited, and arises in a warm and dense region. The OH emission has been modeled using spherically symmetric, non-local, non-LTE radiative transfer models. The models indicate that the bulk of the emission arises from the nuclear region, although some extended contribution from the starburst is not ruled out. The OH abundance in the nuclear region is expected to be ∼ 10 −5 , characteristic of X-ray dominated regions.