Browsing by Author "Ashby, Matthew L. N."

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Beyond Simple AGN Unification with Chandra-observed 3CRR Sources at 0.5 < z < 1
    (2021) Kuraszkiewicz, Joanna; Wilkes, Belinda J.; Atanas, Adam; Buchner, Johannes; McDowell, Jonathan C.; Willner, S. P.; Ashby, Matthew L. N.; Azadi, Mojegan; Barthel, Peter; Haas, Martin; Worrall, Diana M.; Birkinshaw, Mark; Antonucci, Robert; Chini, Rolf; Fazio, Giovanni G.; Lawrence, Charles; Ogle, Patrick
    Low-frequency radio selection finds radio-bright galaxies regardless of the amount of obscuration by gas and dust. We report Chandra observations of a complete 178 MHz-selected, and so orientation-unbiased, sample of 44 0.5 < z < 1 3CRR sources. The sample is comprised of quasars and narrow-line radio galaxies (NLRGs) with similar radio luminosities, and the radio structure serves as both an age and an orientation indicator. Consistent with unification, intrinsic obscuration (measured by N (H), X-ray hardness ratio, and X-ray luminosity) generally increases with inclination. However, the sample includes a population not seen in high-z 3CRR sources: NLRGs viewed at intermediate inclination angles with N (H) < 10(22) cm(-2). Multiwavelength analysis suggests that these objects have lower L/L (Edd) than typical NLRGs at similar orientation. Thus, both orientation and L/L (Edd) are important, and a "radiation-regulated unification" provides a better explanation of the sample's observed properties. In comparison with the 3CRR sample at 1 < z < 2, our lower-redshift sample shows a higher fraction of Compton-thin NLRGs (45% versus 29%) but a similar Compton-thick fraction (20%), implying a larger covering factor of Compton-thin material at intermediate viewing angles and thus a more "puffed-up" torus atmosphere. We posit that this is due to a range of L/L (Edd) extending to lower values in this sample. In contrast, at high redshifts, the narrower range and high L/L (Edd) values allowed orientation (and so simple unification) to dominate the sample's observed properties.
  • Thumbnail Image
    Item
    TO STACK OR NOT TO STACK : SPECTRAL ENERGY DISTRIBUTION PROPERTIES OF Lyα-EMITTING GALAXIES AT z=2.1
    (2014) Vargas, Carlos J.; Bish, Hannah; Acquaviva, Viviana; Gawiser, Eric; Finkelstein, Steven L.; Ciardullo, Robin; Ashby, Matthew L. N.; Feldmeier, John; Ferguson, Henry; Padilla, Nelson; Gronwall, Caryl; Guaita, Lucía; Hagen, Alex; Koekemoer, Anton; Kurczynski, Peter; Newman, Jeffrey A.
  • No Thumbnail Available
    Item
    TO STACK OR NOT TO STACK: SPECTRAL ENERGY DISTRIBUTION PROPERTIES OF Lyα-EMITTING GALAXIES AT z=2.1
    (2014) Vargas, Carlos J.; Bish, Hannah; Acquaviva, Viviana; Gawiser, Eric; Finkelstein, Steven L.; Ciardullo, Robin; Ashby, Matthew L. N.; Feldmeier, John; Ferguson, Henry; Gronwall, Caryl; Guaita, Lucia; Hagen, Alex; Koekemoer, Anton; Kurczynski, Peter; Newman, Jeffrey A.; Padilla, Nelson
    We use the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) GOODS-S multi-wavelength catalog to identify counterparts for 20 Ly alpha emitting (LAE) galaxies at z = 2.1. We build several types of stacked spectral energy distributions (SEDs) of these objects. We combine photometry to form average and median flux-stacked SEDs, and postage-stamp images to form average and median image-stacked SEDs. We also introduce scaled flux stacks that eliminate the influence of variation in overall brightness. We use the SED fitting code SpeedyMC to constrain the physical properties of individual objects and stacks. Our LAEs at z = 2.1 have stellar masses ranging from 2 x 10(7) M-circle dot to 8 x 10(9) M-circle dot (median = 3 x 10(8) M-circle dot), ages ranging from 4 Myr to 500 Myr (median = 100 Myr), and E(B - V) between 0.02 and 0.24 (median = 0.12). Although still low, this represents significantly more dust reddening than has been reported for LAEs at higher redshifts. We do not observe strong correlations between Ly alpha equivalent width (EW) and age or E(B - V). The Ly alpha radiative transfer (q) factors of our sample are predominantly close to one and do not correlate strongly with EW or E(B - V). The absence of strong correlations with EW or q implies that Ly alpha radiative transfer is highly anisotropic and/or prevents Ly alpha photons from scattering in dusty regions. The SED parameters of the flux stacks match the average and median values of the individual objects, with the flux-scaled median SED performing best with uncertainties reduced by a factor of two. Median image-stacked SEDs provide a poor representation of the median individual object, and none of the stacking methods capture the large dispersion of LAE properties.