Looking for bright galaxies born in the early universe is fundamental to investigating the Epoch of Reionization, the era when the first stars and galaxies ionized the intergalactic medium. We ...utilize Hubble Space Telescope pure-parallel imaging to select galaxy candidates at a time 500-650 million years after the Big Bang, which corresponds to redshifts z ∼ 8-10. These data come from the Brightest of Reionizing Galaxies Survey (BoRG) Cycle 22 data set, which consists of pure-parallel imaging in ∼90 different lines of sight that sum up to an area of ∼420 arcmin2. This survey uses five filters and has the advantage (compared to the Cycle 21 BoRG program) of including imaging in the JH140 band, covering continuous wavelengths from the visible to near-infrared (λ = 0.35-1.7 m). This allows us to perform a reliable selection of galaxies at z ≥ 8 using the photometric-redshift technique. We use these galaxy candidates to constrain the bright end of the rest-frame ultraviolet luminosity function in this epoch. These candidates are excellent targets for follow-up observations, particularly with the James Webb Space Telescope.
Research over the past decade has shown diminishing evidence for major galaxy mergers being a dominant mechanism for the growth of supermassive black holes (BHs) in galaxies and the triggering of ...optically or X-ray-selected active galactic nuclei (AGNs). For the first time we test whether such a connection exists at least in the most "plausible" part of parameter space: the highest specific accretion rate broad-line AGNs at the peak epoch of BH activity around z = 2. To that end we analyze two samples-21 AGNs with L/Ledd > 0.7 and 92 stellar mass- and redshift-matched inactive galaxies-observed with HST/WFC3. We remove the AGN point sources from their host galaxies and avoid bias in visual classification by adding and then subtracting mock point sources to and from the comparison galaxies, producing matched residual structures for both sets. The resulting samples are joined and visually ranked according to distortion strength by 10 experts. The ensuing individual rankings are combined into a consensus sequence and from this we derive the merger fractions for both samples. With the merger fractions fm,agn = 0.24 0.09 for the AGN host galaxy sample and fm,ina = 0.19 0.04 for the inactive galaxies, we find no significant difference between the samples. This finding is consistent with previous studies for different AGN populations, and we conclude that even BH growth at the highest specific accretion rates and at the peak of cosmic AGN activity is not predominantly caused by major mergers.
Abstract
Observational studies are increasingly finding evidence against major mergers being the dominant mechanism responsible for triggering an active galactic nucleus (AGN). After studying the ...connection between major mergers and AGNs with the highest Eddington ratios at
z
= 2, we here expand our analysis to
, exploring the same AGN parameter space. Using ESO VLT/FORS2
,
, and color images, we examine the morphologies of 17 galaxies hosting AGNs with Eddington ratios
, and 25 mass- and redshift-matched control galaxies. To match the appearance of the two samples, we add synthetic point sources to the inactive comparison galaxies. The combined sample of AGN and inactive galaxies was independently ranked by 19 experts with respect to the degree of morphological distortion. We combine the resulting individual rankings into multiple overall rankings, from which we derive the respective major merger fractions of the two samples. With a best estimate of
f
m,agn
= 0.41 ± 0.12 for the AGN host galaxies and
f
m,ina
= 0.08 ± 0.06 for the inactive galaxies, our results imply that our AGN host galaxies have a significantly higher merger rate, regardless of the observed wavelength or applied methodology. We conclude that although major mergers are an essential mechanism to trigger local high Eddington ratio AGNs at
, the origin of
of this specific AGN subpopulation still remains unclear.
We have developed a Java-based teaching tool, "Appreciating Hubble at Hyper-speed" ("AHaH"), intended for use by students and instructors in beginning astronomy and cosmology courses, which we have ...made available online. This tool lets the user hypothetically traverse the Hubble Ultra Deep Field (HUDF) in three dimensions at over 500x10^12 times the speed of light, from redshifts z=0 today to z=6, about 1 Gyr after the Big Bang. Users may also view the Universe in various cosmology configurations and two different geometry modes - standard geometry that includes expansion of the Universe, and a static pseudo-Euclidean geometry for comparison. In this paper we detail the mathematical formulae underlying the functions of this Java application, and provide justification for the use of these particular formulae. These include the manner in which the angular sizes of objects are calculated in various cosmologies, as well as how the application's coordinate system is defined in relativistically expanding cosmologies. We also briefly discuss the methods used to select and prepare the images in the application, the data used to measure the redshifts of the galaxies, and the qualitative implications of the visualization - that is, what exactly users see when they "move" the virtual telescope through the simulation. Finally, we conduct a study of the effectiveness in this teaching tool in the classroom, the results of which show the efficacy of the tool, with over 90% approval by students, and provide justification for its further use in a classroom setting.
We have developed a Java-based teaching tool, "Appreciating Hubble at Hyper-speed" (\(\textit{AHaH}\)), intended for use by students and instructors in beginning astronomy and cosmology courses, ...which we have made available online. This tool lets the user hypothetically traverse the Hubble Ultra Deep Field (HUDF) in three dimensions at over \(\sim500\!\times\!10^{12}\) times the speed of light, from redshifts \(z\!=\!0\) today to \(z\!=\!6\), about 1 Gyr after the Big Bang. Users may also view the Universe in various cosmology configurations and two different geometry modes - standard geometry that includes expansion of the Universe, and a static pseudo-Euclidean geometry for comparison. In this paper we detail the mathematical formulae underlying the functions of this Java application, and provide justification for the use of these particular formulae. These include the manner in which the angular sizes of objects are calculated in various cosmologies, as well as how the application's coordinate system is defined in relativistically expanding cosmologies. We also briefly discuss the methods used to select and prepare the images in the application, the data used to measure the redshifts of the galaxies, and the qualitative implications of the visualization - that is, what exactly users see when they "move" the virtual telescope through the simulation. Finally, we conduct a study of the effectiveness in this teaching tool in the classroom, the results of which show the efficacy of the tool, with over \(\sim\)90% approval by students, and provide justification for its further use in a classroom setting.
Looking for bright galaxies born in the early universe is fundamental to investigating the Epoch of Reionization, the era when the first stars and galaxies ionized the intergalactic medium. We ...utilize Hubble Space Telescope pure parallel imaging to select galaxy candidates at a time 500 to 650 million years after the Big Bang, which corresponds to redshifts z ~ 8-10. These data come from the Brightest of Reionizing Galaxies Survey (BoRG) Cycle 22 dataset, which consists of pure-parallel imaging in ~ 90 different lines of sight that sum up to an area of ~ 420 arcmin^2. This survey uses five filters and has the advantage (compared to the Cycle 21 BoRG program) of including imaging in the JH140 band, covering continuous wavelengths from the visible to near-infrared (lambda = 0.35um - 1.7um). This allows us to perform reliable selection of galaxies at z>8 using the photometric redshift technique. We use these galaxy candidates to constrain the bright end of the rest-frame ultraviolet luminosity function in this epoch. These candidates are excellent targets for follow-up observations, particularly with the James Webb Space Telescope.
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.
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