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Browsing Astronomy by Subject "active galaxies"

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    THE COOL SIDE OF GALACTIC WINDS: EXPLORATION WITH HERSCHEL-PACS AND SPITZER-IRS
    (2020) Stone, Myra; Veilleux, Sylvain; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Galactic-scale outflows driven by starbursts and/or active galactic nuclei (AGN) are key ingredients to theoretical models and numerical simulations of galaxy assembly and evolution. The feedback induced by the presence of these outflows (or winds) may affect the evolution and formation of a galaxy by regulating the amount of cold, dense gas responsible for star formation and black hole accretion. We present the results from a systematic search for galactic-scale, molecular (OH 119 μm) outflows in a sample of 52 Local Volume (d < 50 Mpc) Burst Alert Telescope detected active galactic nuclei (BAT AGN) with Herschel-PACS. We combine the results from our analysis of the BAT AGN with the published Herschel/PACS data of 43 nearby (z < 0.3) galaxy mergers, mostly ultraluminous infrared galaxies (ULIRGs) and QSOs. Our data show that both the starburst and AGN contribute to driving OH outflows, but the fastest OH winds require AGN with quasar-like luminosities. We also analyze Spitzer InfraRed Spectrograph (IRS) observations of the OH 35 μm feature in 15 nearby (z < 0.06) (ultra-)luminous infrared galaxies (U/LIRGs). The measured OH 35 μm equivalent widths are used to compute an average OH column density which is then compared to the hydrogen column density for a typical optical depth at 35 μm of ∼0.5 and gas-to-dust ratio of 125 to derive an OH−to−H abundance ratio of X_{OH} = 1.01 ± 0.15 × 10^{−6}. The OH 35 μm line profiles predicted from published radiative transfer models constrained by observa- tions of OH 65, 79, 84, and 119 μm in five objects are found to be consistent with the IRS OH 35 μm spectra. Finally, we analyze Herschel-PACS observations of five atomic fine-structure transition lines ([O I] 63 μm, [O III] 88 μm, [N II] 122 μm, [O I] 145 μm, and [C II] 158 μm) in seven nearby (d < 16 Mpc) galaxies with well-known galactic- scale outflows (Cen A, Circinus, M 82, NGC 253, NGC 1068, NGC 3079, and NGC 4945). With this suite of atomic emission lines, we investigate the cool neutral atomic (T ~ 10^3 K) and warm ionized (T ~ 10^4 K) gas phases within each outflow. The outflows in the Herschel data are spatially isolated from the galactic disk based on the kinematic signatures of the outflows. The spatial distribution and physical properties of the outflows detected in the Herschel data are compared with published results at other wavelengths. For completeness, an analysis of the molecular gas traced by OH 119 μm is also presented.
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    Neutral Gas Outflows and Inflows in Local AGN & High-z Lyman-alpha Emitters in COSMOS
    (2013) Krug, Hannah Bowen; Veilleux, Sylvain; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis is composed of two parts: (1) a search for neutral gas outflows and inflows in local active galactic nuclei (AGN) and ultraluminous infrared galaxies (ULIRGs), and (2) a deep and wide imaging search for high-redshift Lyman-alpha emitters (LAEs). In the first part, we utilize the R-C spectrograph on the Mayall 4m telescope at Kitt Peak National Observatory (KPNO) to look for Na I D absorption. Galactic outflows are thought to play a major role in galactic feedback and evolution, and previous studies of neutral gas have shown that galactic winds occur in most galaxies with high infrared (IR) luminosities. However, in composite systems where a starburst coexists with an active galactic nucleus (AGN), it is unclear whether the starburst or the AGN is driving the outflows. This thesis attempts to answer that question by looking at samples of Seyfert galaxies, Palomar-Green quasistellar objects (PG QSOs), and ULIRGs. We first describe the results from a search for Na I D outflows in 35 IR-faint Seyferts. We find that the outflow detection rates for IR-faint Seyferts are substantially lower than those of IR-luminous Seyferts. The outflow kinematics of Seyfert 2s resemble those of starburst galaxies, while the outflow velocities in Seyfert 1s are significantly larger. Taken together, these results suggest that the AGN does not play a significant role in driving the outflows in most Seyferts, except the high velocity outflows seen in Seyfert 1s. We also find high rates of detection of inflows in IR-faint Seyferts. We then perform the same analysis on a sample of 28 PG QSOs and 10 ULIRGs; this sample was taken from a survey of gas-rich mergers. When we combine our data with our Seyfert study results, as well as previous work, we note three important trends. We find that outflows in IR-luminous AGN and IR-luminous starbursts appear to be driven by fundamentally different processes, the AGN and star formation, respectively. We find the same distinction for outflows in AGN with optical spectral types of Type 1 (AGN) and Type 2 (star formation). We note fundamental differences between outflows in objects which have already undergone mergers versus those which have not. In the second part of this thesis, we search for z = 7.7 LAEs in the COSMOS field. These objects are useful probes of the epoch of reionization, as the Lya line should be attenuated by the intergalactic medium (IGM) at low to moderate neutral hydrogen fractions (xHI). We have utilized two ultra-narrowband filters on the NEWFIRM camera in order to isolate LAEs at z = 7.7. We find 5-sigma detections of four candidate LAEs in a survey volume of 2.8 x 10^4 Mpc^3. Using these results to construct a Lya luminosity function (LF) and comparing to previously established LFs at z = 5.7 and z = 6.5, we find no conclusive evidence for evolution of xHI over 5.7 < z < 7.7. Finally, we use a combination of imaging and spectroscopy to follow up those results, noting that, while imaging can rule out a candidate from being considered a high-redshift LAE, only spectroscopy can confirm that a target is indeed at z = 7.7. Imaging follow-up has essentially ruled out one candidate. We then perform spectroscopic follow-up with GNIRS on the Gemini-North telescope on our second brightest candidate. We fail to detect that candidate after 2.5 hours of integration; spectroscopic follow-up performed by collaborators on our two brightest candidates also yielded non-detections. We are thus left with only one viable z = 7.7 candidate. Such null results are consistent with other attempts detailed in the literature, implying that reionization is still ongoing.