Limits to Rest-frame Ultraviolet Emission from Far-infrared-luminous z ≃ 6 Quasar Hosts
Madeline A. MarshallM. MechtleyRogier A. WindhorstSeth H. CohenRolf A. JansenLinhua JiangVictoria JonesJ. Stuart B. WyitheXiaohui FanNimish P. HathiK. JahnkęWilliam C. KeelAnton M. KoekemoerVictor MarianKeven RenJ. RobinsonH. J. A. RöttgeringRussell E. RyanEvan ScannapiecoDonald P. SchneiderGlenn SchneiderBrent M. SmithHaojing Yan
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We report on a Hubble Space Telescope search for rest-frame ultraviolet emission from the host galaxies of five far-infrared-luminous $z\simeq{}6$ quasars and the $z=5.85$ hot-dust free quasar SDSS J0005-0006. We perform 2D surface brightness modeling for each quasar using a Markov-Chain Monte-Carlo estimator, to simultaneously fit and subtract the quasar point source in order to constrain the underlying host galaxy emission. We measure upper limits for the quasar host galaxies of $m_J>22.7$ mag and $m_H>22.4$ mag, corresponding to stellar masses of $M_\ast<2\times10^{11}M_\odot$. These stellar mass limits are consistent with the local $M_{\textrm{BH}}$-$M_\ast$ relation. Our flux limits are consistent with those predicted for the UV stellar populations of $z\simeq6$ host galaxies, but likely in the presence of significant dust ($\langle A_{\mathrm{UV}}\rangle\simeq 2.6$ mag). We also detect a total of up to 9 potential $z\simeq6$ quasar companion galaxies surrounding five of the six quasars, separated from the quasars by 1.4''-3.2'', or 8.4-19.4 kpc, which may be interacting with the quasar hosts. These nearby companion galaxies have UV absolute magnitudes of -22.1 to -19.9 mag, and UV spectral slopes $\beta$ of -2.0 to -0.2, consistent with luminous star-forming galaxies at $z\simeq6$. These results suggest that the quasars are in dense environments typical of luminous $z\simeq6$ galaxies. However, we cannot rule out the possibility that some of these companions are foreground interlopers. Infrared observations with the James Webb Space Telescope will be needed to detect the $z\simeq6$ quasar host galaxies and better constrain their stellar mass and dust content.We present initial results from a Chandra survey of a complete sample of the 8 nearest (z <= 0.04) ultraluminous IR galaxies (ULIRGs), and also include the IR-luminous galaxy NGC 6240 for comparison. In this paper we use the hard X-rays (2-8 kev) to search for the possible presence of an obscured AGN. In every case, a hard X-ray source is detected in the nuclear region. If we divide the sample according to the optical/IR spectroscopic classification (starburst vs. AGN), we find that the 5 ``starburst'' ULIRGs have hard X-ray luminosities about an order-of-magnitude smaller than the 3 ``AGN'' ULIRGs. NGC 6240 has an anomalously high hard X-ray luminosity compared to the ``starburst'' ULIRGs. The Fe Kalpha line is convincingly detected in only two ULIRGs. The weakness of the Fe-K emission in these ULIRGs generally suggests that the hard X-ray spectrum is not dominated by reflection from high N_H neutral material. The hard X-ray continuum flux ranges from a few X 10^3 to a few X 10^-5 of the far-IR flux, similar to values in pure starbursts, and several orders-of-magnitude smaller than in Compton-thin AGN. The upper limits on the ratio of the Fe Kalpha to far-IR flux are below the values measured in Compton-thick type 2 Seyfert galaxies. While very large column densities of molecular gas are observed in the nuclei of these galaxies, we find no evidence that the observed X-ray sources are obscured by Compton-thick material. Thus, our new hard X-ray data do not provide direct evidence that powerful ``buried quasars'' dominate the overall energetics of most ultraluminous infrared galaxies.
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We present HST (WFPC2 and FOC) images and UV GHRS spectra plus ground-based optical spectra of four Luminous Infrared Galaxies (LIRGs) that have Seyfert 2 nuclei (Mrk 477, NGC 7130, NGC 5135 and IC 3639). The data provide direct evidence of the existence of a central nuclear starburst that dominates the UV and optical light and are dusty and compact. The bolometric luminosity of 10$^{10}$ Lsol of these starbursts is similar to the estimated bolometric luminosities of their obscured Seyfert 1 nuclei, and thus they contribute in the same amount to the overall energetics of these galaxies. An extended work based on ground-based optical spectra of the 20 brightest nuclei known indicate that at least 40% of the Seyfert 2 galaxies harbor a nuclear starburst. The eight Seyfert 2 nuclei that harbor a starburst are strong IR emitters. This suggests that nuclear starbursts can make a significant contribution or even dominate the UV and optical light of LIRGs.
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Previous studies of the Na I D interstellar absorption line doublet have shown that galactic winds occur in most galaxies with high infrared luminosities. However, in infrared-bright composite systems where a starburst coexists with an active galactic nucleus (AGN), it is unclear whether the starburst, the AGN, or both are driving the outflows. The present paper describes the results from a search for outflows in 35 infrared-faint Seyferts with 10{sup 9.9}< L{sub IR}/L{sub sun} < 10{sup 11}, or, equivalently, star formation rates (SFRs) of approx0.4-9 M{sub sun} yr{sup -1}, to attempt to isolate the source of the outflow. We find that the outflow detection rates for the infrared-faint Seyfert 1s (6%) and Seyfert 2s (18%) are lower than previously reported for infrared-luminous Seyfert 1s (50%) and Seyfert 2s (45%). The outflow kinematics of infrared-faint and infrared-bright Seyfert 2 galaxies resemble those of starburst galaxies, while the outflow velocities in Seyfert 1 galaxies are significantly larger. Taken together, these results suggest that the AGN does not play a significant role in driving the outflows in most infrared-faint and infrared-bright systems, except the high-velocity outflows seen in Seyfert 1 galaxies. Another striking result of this study is the high rate of detectionmore » of inflows in infrared-faint galaxies (39% of Seyfert 1s, 35% of Seyfert 2s), significantly larger than in infrared-luminous Seyferts (15%). This inflow may be contributing to the feeding of the AGN in these galaxies, and potentially provides more than enough material to power the observed nuclear activity over typical AGN lifetimes.« less
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This paper presents an analysis of moderately large samples of type 1 and 2 Seyfert galaxies through optical observations and far-infrared IRAS data, also taking into account theoretical color indices derived from dust emission models. The galaxies in the samples cover a rather large interval in far-infrared luminosity, i.e., 7.6 ≤ log (LIR/L☉) ≤ 12.6. We show that both types of Seyferts have approximately the same distribution of number of objects with a given LIR. Galaxies with similar far-infrared color indices α(100, 60) are grouped together, and the corresponding average color indices are interpreted in terms of a simple model in which the observed colors result from the combination of dust directly heated by the active galactic nucleus with a component from the host galaxy represented by the emission of cool dust. On the basis of the average IRAS colors of the derived groups, we show that type 1 and 2 Seyfert galaxies are undistinguishable from each other. From the luminosity ratios LIR/LHα and LIR/L[O III], we show that basically the same model can be applied to both types of Seyfert, only allowing for the variation of model conditions: type 2 Seyferts would be like type 1 Seyferts but with the Seyfert nucleus and broad line region more effectively "hidden" by dust.
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Combining the AKARI Point Source Catalog and the 37-month Monitor of All-sky X-ray Image (MAXI) catalog, the infrared and X-ray properties of nearby active galactic nuclei were investigated. The 37-month MAXI catalog tabulates 100 nearby Seyfert galaxies, 73 of which are categorized into Seyfert I galaxies. Among these Seyfert galaxies, 69 ones were found to have an AKARI infrared counterpart. For the Seyfert I galaxies in this sample, a well-known correlation was found between the infrared and X-ray luminosities. However, the observed X-ray luminosity of the Seyfert II galaxies tends to be lower for the infrared luminosity than the Seyfert I galaxies. This suggests that the X-ray absorption is significant in the Seyfert II galaxies. The Seyfert II galaxies seem to have a bimodal distribution of the IR color between $18{\mu}m$ and $90{\mu}m$ . Especially, a large fraction of the Seyfert II galaxies exhibits a redder IR color than the Seyfert I galaxies. A possible origin of the redder IR color is briefly discussed, in relation to the star formation activity in the host galaxy, and to the X-ray absorption.
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A sensitive observation of the CO J = 1-0 molecular line emission in the host galaxy of GRB 030329 (z = 0.1685) has been performed using the Nobeyama Millimeter Array to detect molecular gas and hidden star formation. No sign of CO emission was found, which invalidates our previous report of the presence of molecular gas. The 3 σ upper limit on the CO line luminosity (L) of the host galaxy is 6.9 × 108 K km s-1 pc2. The lower limit to the host galaxy's metallicity is estimated to be 12 + log (O/H) ~ 7.9, which yields a conversion factor from CO line luminosity to H2 of αCO = 40 M☉ (K km s-1 pc2)-1. Assuming this factor, the 3 σ upper limit on the molecular gas mass of the host galaxy is 2.8 × 1010 M☉. Based on the Schmidt law, the 3 σ upper limit on the total star formation rate (SFR) of the host galaxy is estimated to be 38 M☉ yr-1. These results independently confirm inferences from previous observations in the optical, submillimeter, and X-ray bands, which regard this host galaxy as a compact dwarf and not a massive, aggressively star-forming galaxy. Finally, the SFRs of GRB host galaxies, estimated using various techniques immune to dust obscuration, including our CO luminosity measurements, are compared with the SFRs of the same galaxies estimated using extinction-corrected optical/UV tracers. We show that most of the SFRs measured in extinction-free wavelengths, including positive detections and upper limits, are larger by from 1 to a few orders of magnitude compared with the SFRs of the same galaxies measured by optical/UV tracers.
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Observations from the HERschel Inventory of the Agents of Galaxy Evolution (HERITAGE) have been used to identify dusty populations of sources in the Large and Small Magellanic Clouds (LMC and SMC). We conducted the study using the HERITAGE catalogs of point sources available from the Herschel Science Center from both the Photodetector Array Camera and Spectrometer (PACS; 100 and 160 μm) and Spectral and Photometric Imaging Receiver (SPIRE; 250, 350, and 500 μm) cameras. These catalogs are matched to each other to create a Herschel band-merged catalog and then further matched to archival Spitzer IRAC and MIPS catalogs from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and SAGE-SMC surveys to create single mid- to far-infrared (far-IR) point source catalogs that span the wavelength range from 3.6 to 500 μm. There are 35,322 unique sources in the LMC and 7503 in the SMC. To be bright in the FIR, a source must be very dusty, and so the sources in the HERITAGE catalogs represent the dustiest populations of sources. The brightest HERITAGE sources are dominated by young stellar objects (YSOs), and the dimmest by background galaxies. We identify the sources most likely to be background galaxies by first considering their morphology (distant galaxies are point-like at the resolution of Herschel) and then comparing the flux distribution to that of the Herschel Astrophysical Terahertz Large Area Survey (ATLAS) survey of galaxies. We find a total of 9745 background galaxy candidates in the LMC HERITAGE images and 5111 in the SMC images, in agreement with the number predicted by extrapolating from the ATLAS flux distribution. The majority of the Magellanic Cloud-residing sources are either very young, embedded forming stars or dusty clumps of the interstellar medium. Using the presence of 24 μm emission as a tracer of star formation, we identify 3518 YSO candidates in the LMC and 663 in the SMC. There are far fewer far-IR bright YSOs in the SMC than the LMC due to both the SMC's smaller size and its lower dust content. The YSO candidate lists may be contaminated at low flux levels by background galaxies, and so we differentiate between sources with a high ("probable") and moderate ("possible") likelihood of being a YSO. There are 2493/425 probable YSO candidates in the LMC/SMC. Approximately 73% of the Herschel YSO candidates are newly identified in the LMC, and 35% in the SMC. We further identify a small population of dusty objects in the late stages of stellar evolution including extreme and post-asymptotic giant branch, planetary nebulae, and supernova remnants. These populations are identified by matching the HERITAGE catalogs to lists of previously identified objects in the literature. Approximately half of the LMC sources and one quarter of the SMC sources are too faint to obtain accurate ample FIR photometry and are unclassified.
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Observations of the afterglows of long gamma-ray bursts (GRBs) allow the study of star-forming galaxies across most of cosmic history. Here we present observations of GRB 111008A from which we can measure metallicity, chemical abundance patterns, dust-to-metals ratio and extinction of the GRB host galaxy at z=5.0. The host absorption system is a damped Lyman-alpha absorber (DLA) with a very large neutral hydrogen column density of log N(HI)/cm^(-2) = 22.30 +/- 0.06, and a metallicity of [S/H]= -1.70 +/- 0.10. It is the highest redshift GRB with such a precise metallicity measurement. The presence of fine-structure lines confirms the z=5.0 system as the GRB host galaxy, and makes this the highest redshift where Fe II fine-structure lines have been detected. The afterglow is mildly reddened with A_V = 0.11 +/- 0.04 mag, and the host galaxy has a dust-to-metals ratio which is consistent with being equal to or lower than typical values in the Local Group.
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We have selected an all--sky sample of 893 galaxies from the IRAS FSC--2, defined by a total (ADDSCAN) 12um flux limit of 0.22~Jy. Completeness is verified to 0.30~Jy, below which we have quantified the incompleteness down to 0.22~Jy for our statistical analysis. ¶The Seyfert subsample is the largest unbiased sample of (118) Seyfert galaxies ever assembled and is complete not only to 0.30~Jy at 12um, but also with respect to a bolometric flux limit of $\sim2.0\times10^{-10}$~(cgs). The average $V/V_{max}$ for the full sample, corrected for incompleteness at low fluxes, is $0.51\pm0.04$, while that for Seyferts is $0.46\pm0.10$, suggesting that several Seyferts are yet to be identified in our sample. The AGN luminosity functions (LFs) are more complete than those of the optically selected CfA Seyfert galaxies for all luminosities and AGN types. ¶The 60um LF for a complete 60um--flux--limited (at 8.3~Jy) subsample of 235 galaxies is in satisfactory agreement with those derived from the bright galaxy sample (BGS) and the deep high--galactic latitude sample, both selected at 60um. Over the high lum. range where our sample and the BGS overlap, however, our space densities are systematically lower by a factor of $\sim 1.5$, whereas at low lum. our space densities are higher by about the same amount. Comparable results are obtained when comparing the far--IR LF of our entire sample with the one derived from the BGS. This is not unexpected, because of the bias towards high-luminosity spirals caused by selection at 60um.
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The energy sources of nine infrared luminous galaxies (IRLGs) are diagnosed based on their ground-based 3-4 μm spectra. Both the equivalent width of the 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission feature and the 3.3 μm PAH to far-infrared luminosity ratio (L3.3/LFIR) are analyzed. Assuming that nuclear compact starburst activity in these sources produces the 3.3 μm PAH emission as strongly as that in starburst galaxies with lower far-infrared luminosities, the following results are found. For six IRLGs, both the observed equivalent widths and the L3.3/LFIR ratios are too small to explain the bulk of their far-infrared luminosities by compact starburst activity, indicating that active galactic nucleus (AGN) activity is a dominant energy source. For the other three IRLGs, while the 3.3 μm PAH equivalent widths are within the range of starburst galaxies, the L3.3/LFIR ratios after correction for screen dust extinction are a factor of ~3 smaller. The uncertainty in the dust extinction correction factor and in the scatter of the intrinsic L3.3/LFIR ratios for starburst galaxies does not allow a determination of the ultimate energy sources for these three IRLGs.
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