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Register a new userThe Relationship Between Intergalactic HI/OVI and Nearby (z<0.017) Galaxies
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We analyze intergalactic HI and OVI absorbers with v<5000 km/s in HST and FUSE spectra of 76 AGNs. The baryons traced by HI/OVI absorption are clearly associated with the extended surroundings of galaxies; for impact parameters <400 kpc they are ~5 times more numerous as those inside the galaxies. This large reservoir of matter likely plays a major role in galaxy evolution. We tabulate the fraction of absorbers having a galaxy of a given luminosity within a given impact parameter (rho) and velocity difference (Dv), as well as the fraction of galaxies with an absorber closer than a given rho and Dv. We identify possible void absorbers (rho>3 Mpc to the nearest L* galaxy), although at v<2500 km/s all absorbers are within 1.5 Mpc of an L>0.1 L* galaxy. The absorber properties depend on rho, but the relations are not simple correlations. For four absorbers with rho=50-350 kpc from an edge-on galaxy with known orientation of its rotation, we find no clear relation between absorber velocities and the rotation curve of the underlying galaxy. For rho<350 kpc the covering factor of Ly-alpha (OVI) around L>0.1 L* galaxies is 100% for field galaxies and 65% for group galaxies; 50% of galaxy groups have associated Ly-alpha. All OVI absorbers occur within 550 kpc of an L>0.25 L* galaxy. The properties of three of 14 OVI absorbers are consistent with photoionization, for five the evidence points to collisional ionization; the others are ambiguous. The fraction of broad Ly-alpha lines increases from z=3 to z=0 and with decreasing impact parameter, consistent with the idea that gas inside ~500 kpc from galaxies is heating up, although alternative explanations can not be clearly excluded.
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We present estimates of black hole accretion rates and nuclear, extended, and total star-formation rates for a complete sample of Seyfert galaxies. Using data from the Spitzer Space Telescope, we measure the active galactic nucleus (AGN) luminosity using the [O IV] 25.89 micron emission line and the star-forming luminosity using the 11.3 micron aromatic feature and extended 24 micron continuum emission. We find that black hole growth is strongly correlated with nuclear (r<1 kpc) star formation, but only weakly correlated with extended (r>1 kpc) star formation in the host galaxy. In particular, the nuclear star-formation rate (SFR) traced by the 11.3 micron aromatic feature follows a relationship with the black hole accretion rate (BHAR) of the form SFRproptoBHAR^0.8, with an observed scatter of 0.5 dex. This SFR-BHAR relationship persists when additional star formation in physically matched r=1 kpc apertures is included, taking the form SFRproptoBHAR^0.6. However, the relationship becomes almost indiscernible when total SFRs are considered. This suggests a physical connection between the gas on sub-kpc and sub-pc scales in local Seyfert galaxies that is not related to external processes in the host galaxy. It also suggests that the observed scaling between star formation and black hole growth for samples of AGNs will depend on whether the star formation is dominated by a nuclear or extended component. We estimate the integrated black hole and bulge growth that occurs in these galaxies and find that an AGN duty cycle of 5-10% would maintain the ratio between black hole and bulge masses seen in the local universe.
High resolution, multi-wavelength maps of a sizeable set of nearby galaxies have made it possible to study how the surface densities of HI, H2 and star formation rate (Sigma_HI, Sigma_H2, Sigma_SFR) relate on scales of a few hundred parsecs. At these scales, individual galaxy disks are comfortably resolved, making it possible to assess gas-SFR relations with respect to environment within galaxies. Sigma_H2, traced by CO intensity, shows a strong correlation with Sigma_SFR and the ratio between these two quantities, the molecular gas depletion time, appears to be constant at about 2Gyr in large spiral galaxies. Within the star-forming disks of galaxies, Sigma_SFR shows almost no correlation with Sigma_HI. In the outer parts of galaxies, however, Sigma_SFR does scale with Sigma_HI, though with large scatter. Combining data from these different environments yields a distribution with multiple regimes in Sigma_gas - Sigma_SFR space. If the underlying assumptions to convert observables to physical quantities are matched, even combined datasets based on different SFR tracers, methodologies and spatial scales occupy a well define locus in Sigma_gas - Sigma_SFR space.
We present the Very Large Array survey of Advanced Camera for Surveys Nearby Galaxy Survey Treasury galaxies (VLA-ANGST). VLA-ANGST is a National Radio Astronomy Observatory Large Program consisting of high spectral (0.6-2.6 km/s) and spatial (~6) resolution observations of neutral, atomic hydrogen (HI) emission toward 35 nearby dwarf galaxies from the ANGST survey. ANGST is a systematic HST survey to establish a legacy of uniform multi-color photometry of resolved stars for a volume-limited sample of nearby galaxies (Dlesssim4 Mpc). VLA-ANGST provides VLA HI observations of the sub-sample of ANGST galaxies with recent star formation that are observable from the northern hemisphere and that were not observed in the The HI Nearby Galaxy Survey (THINGS). The overarching scientific goal of VLA-ANGST is to investigate fundamental characteristics of the neutral interstellar medium (ISM) of dwarf galaxies. Here we describe the VLA observations, the data reduction, and the final VLA-ANGST data products. We present an atlas of the integrated HI maps, the intensity-weighted velocity fields, the second moment maps as a measure for the velocity dispersion of the HI, individual channel maps, and integrated HI spectra for each VLA-ANGST galaxy. We closely follow the observational setup and data reduction of THINGS to achieve comparable sensitivity and angular resolution. A major difference, however, is the high velocity resolution of the VLA-ANGST observations (0.65 and 1.3km/s for the majority of the galaxies). The VLA-ANGST data products are made publicly available at: https://science.nrao.edu/science/surveys/vla-angst. With available star formation histories from resolved stellar populations and lower resolution ancillary observations from the FIR to the UV, VLA-ANGST will enable detailed studies of the relationship between the ISM and star formation in dwarf galaxies on a ~100 pc scale.
Aims. Our aim is to estimate the intergalactic medium transmission towards UV-selected star-forming galaxies at redshift 4 and above and study the effect of the dust attenuation on these measurements. Methods. The ultra-violet spectrum of high redshift galaxies is a combination of their intrinsic emission and the effect of the Inter-Galactic medium (IGM) absorption along their line of sight. Using data coming from the unprecedented deep spectroscopy from the VANDELS ESO public survey carried out with the VIMOS instrument we compute both the dust extinction and the mean transmission of the IGM as well as its scatter from a set of 281 galaxies at z>3.87. Because of a degeneracy between the dust content of the galaxy and the IGM, we first estimate the stellar dust extinction parameter E(B-V) and study the result as a function of the dust prescription. Using these measurements as constraint for the spectral fit we estimate the IGM transmission Tr(Lyalpha). Both photometric and spectroscopic SED fitting are done using the SPectroscopy And photometRy fiTting tool for Astronomical aNalysis (SPARTAN) that is able to fit the spectral continuum of the galaxies as well as photometric data. Results. Using the classical Calzettis attenuation law we find that E(B-V) goes from 0.11 at z=3.99 to 0.08 at z=5.15. These results are in very good agreement with previous measurements from the literature. We estimate the IGM transmission and find that the transmission is decreasing with increasing redshift from Tr(Lyalpha)=0.53 at z=3.99 to 0.28 at z=5.15. We also find a large standard deviation around the average transmission that is more than 0.1 at every redshift. Our results are in very good agreement with both previous measurements from AGN studies and with theoretical models.
We analyze the association of galaxies to Lya and OVI absorption, the most commonly detected transitions in the low-z intergalactic medium (IGM), in the fields of 14 quasars with z_em = 0.06-0.57. Confirming previous studies, we observe a high covering fraction for Lya absorption to impact parameter rho = 300kpc: 33/37 of our L>0.01L* galaxies show Lya equivalent width W_Lya>50mA. Galaxies of all luminosity L>0.01L* and spectral type are surrounded by a diffuse and ionized circumgalactic medium (CGM), whose baryonic mass is estimated at ~10^(10.5 +/- 0.3) Msun for a constant N_H. The virialized halos and extended CGM of present-day galaxies are responsible for most strong Lya absorbers (W_Lya > 300mA) but cannot reproduce the majority of observed lines in the Lya forest. We conclude that the majority of Lya absorption with W_Lya=30-300mA occurs in the cosmic web predicted by cosmological simulations and estimate a characteristic width for these filaments of ~400kpc. Regarding OVI, we observe a near unity covering fraction to rho=200kpc for L>0.1L* galaxies and to rho = 300kpc for sub-L* (0.1 L*<L<L*) galaxies. Similar to our Lya results, stronger OVI systems (W_OVI > 70mA) arise in the virialized halos of L>0.1L* galaxies. Unlike Lya, the weaker OVI systems (W_OVI~30mA) arise in the extended CGM of sub-L* galaxies. The majority of OVI gas observed in the low-z IGM is associated with a diffuse medium surrounding individual galaxies with L~0.3L*, and rarely originates in the so-called warm-hot IGM (WHIM) predicted by cosmological simulations.
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