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234 results on '"Reines, A. E."'

51. NuSTAR Observations of a Heavily X-Ray-obscured AGN in the Dwarf Galaxy J144013+024744

Author

Ansh, Shrey, primary, Chen, Chien-Ting J., additional, Brandt, W. N., additional, Hood, Carol E., additional, Kammoun, E. S., additional, Lansbury, G., additional, Paltani, Stéphane, additional, Reines, Amy E., additional, Ricci, C., additional, Swartz, Douglas A., additional, Trump, Jonathan R., additional, Vito, F., additional, and Hickox, Ryan C., additional

Published
2023
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60. The AGN Fraction in Dwarf Galaxies from eROSITA: First Results and Future Prospects

Author

Latimer, Colin J., Reines, Amy E., Bogdan, Akos, Kraft, Ralph, Latimer, Colin J., Reines, Amy E., Bogdan, Akos, and Kraft, Ralph

Abstract

Determining the fraction of nearby dwarf galaxies hosting massive black holes (BHs) can inform our understanding of the origin of "seed" black holes at high redshift. Here we search for signatures of accreting massive BHs in a sample of dwarf galaxies ($M_\star \le 3 \times 10^9~M_\odot$, $z \leq 0.15$) selected from the NASA-Sloan Atlas (NSA) using X-ray observations from the eROSITA Final Equatorial Depth Survey (eFEDS). On average, our search is sensitive to active galactic nuclei (AGNs) in dwarf galaxies that are accreting at $\gtrsim 1\%$ of their Eddington luminosity. Of the ${\sim}28,000$ X-ray sources in eFEDS and the $495$ dwarf galaxies in the NSA within the eFEDS footprint, we find six galaxies hosting possible active massive BHs. If the X-ray sources are indeed associated with the dwarf galaxies, the X-ray emission is above that expected from star formation, with X-ray source luminosities of $L_{0.5-8~\textrm{keV}} \sim 10^{39\textrm{-}40}$ erg s$^{-1}$. Additionally, after accounting for chance alignments of background AGNs with dwarf galaxies, we estimate there are between 0-9 real associations between dwarf galaxies and X-ray sources in the eFEDS field at the $95\%$ confidence level. From this we find an upper limit on the eFEDS-detected dwarf galaxy AGN fraction of $\le 1.8\%$, which is broadly consistent with similar studies at other wavelengths. We extrapolate these findings from the eFEDS sky coverage to the planned eROSITA All-Sky Survey and estimate that upon completion, the all-sky survey could yield as many as ${\sim}1350$ AGN candidates in dwarf galaxies at low redshift., Comment: 7 pages, 3 figures, accepted for publication in ApJ Letters

Published
2021
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61. A Chandra and HST View of WISE-Selected AGN Candidates in Dwarf Galaxies

Author

Latimer, Colin J., Reines, Amy E., Hainline, Kevin N., Greene, Jenny E., Stern, Daniel, Latimer, Colin J., Reines, Amy E., Hainline, Kevin N., Greene, Jenny E., and Stern, Daniel

Abstract

Reliably identifying active galactic nuclei (AGNs) in dwarf galaxies is key to understanding black hole demographics at low masses and constraining models for black hole seed formation. Here we present Chandra X-ray Observatory observations of eleven dwarf galaxies that were chosen as AGN candidates using Wide-field Infrared Survey Explorer (WISE) mid-infrared (mid-IR) color-color selection. Hubble Space Telescope images are also presented for ten of the galaxies. Based on Sloan Digital Sky Survey spectroscopy, six galaxies in our sample have optical evidence for hosting AGNs and five are classified as star-forming. We detect X-ray point sources with luminosities above that expected from X-ray binaries in the nuclei of five of the six galaxies with optical evidence of AGNs. However, the X-ray emission from these AGNs is generally much lower than expected based on AGN scaling relations with infrared and optical tracers. We do not find compelling evidence for AGNs in the five optically-selected star-forming galaxies despite having red mid-IR colors. Only two are detected in X-rays and their properties are consistent with stellar-mass X-ray binaries. Based on this multiwavelength study, we conclude that two-color mid-IR AGN diagnostics at the resolution of WISE cannot be used to reliably select AGNs in optically-star-forming dwarf galaxies. Future observations in the infrared with the James Webb Space Telescope offer a promising path forward., Comment: 16 pages, 8 figures, accepted for publication in ApJ

Published
2021
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66. Populating the low-mass end of the $M_{\rm BH}-��_{\ast}$ relation

Author

Baldassare, Vivienne F., Dickey, Claire, Geha, Marla, and Reines, Amy E.

Subjects
Astrophysics::High Energy Astrophysical Phenomena, Astrophysics of Galaxies (astro-ph.GA), Astrophysics::Solar and Stellar Astrophysics, FOS: Physical sciences, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

We present high resolution spectroscopy taken with the Keck Echellete Spectrograph and Imager to measure stellar velocity dispersions for eight active dwarf galaxies ($M_{\ast}, Accepted to The Astrophysical Journal Letters

Published
2020
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71. Ultraviolet+Infrared Star Formation Rates: Hickson Compact Groups with Swift and SPitzer

Author

Tzanavaris, P, Hornschemeier, A. E, Gallagher, S. C, Johnson, K. E, Gronwall, C, Immler, S, Reines, A. E, Hoversten, E, and Charlton, J. C

Subjects
Astrophysics
Abstract

We present Swift UVOT ultraviolet (UV; 1600-3000 A) data with complete three-band UV photometry for a sample of 41 galaxies in 11 nearby (<4500 km/s) Hickson Compact Groups (HCGs) of galaxies. We use UVOT uvw2-band (2000A) photometry to estimate the dust-unobscured component, SFR(sub uv), of the total star formation rate, SFR(sub TOTAL). We use Spitzer MIPS 24 micron photometry to estimate SFR(sub IR), the component of SFR(sub TOTAL) that suffers dust extinction in the UV and is re-emitted in the IR. By combining the two components, we obtain SFR(sub TOTAL) estimates for all HCG galaxies. We obtain total stellar mass, M(sub *) estimates by means of Two Micron All Sky Survey K(sub s)-band luminosities, and use them to calculate specific star formation rates, SSFR is identical with SFR(sub TOTAL)/ M (sub *). SSFR values show a clear and significant bimodality, with a gap between low (approximately <3.2 x 10(exp -11) / yr) and high-SSFR (approximately > 1.2 x lO)exp -10)/yr) systems. We compare this bimodality to the previously discovered bimodality in alpha-IRAC, the MIR activity index from a power-law fit to the Spitzer IRAC 4.5-8 micron data for these galaxies. We find that all galaxies with alpha-IRAC <= 0 (> 0) are in the high- (low-) SSFR locus, as expected if high levels of star-forming activity power MIR emission from polycyclic aromatic hydrocarbon molecules and a hot dust continuum. Consistent with this finding, all elliptical/SO galaxies are in the low-SSFR locus, while 22 out of 24 spirals / irregulars are in the high-SSFR locus, with two borderline cases. We further divide our sample into three subsamples (I, II, and III) according to decreasing H I richness of the parent galaxy group to which a galaxy belongs. Consistent with the SSFR and alpha-IRAC bimodality, 12 out of 15 type I (11 out of 12 type III) galaxies are in the high- (low-) SSFR locus, while type II galaxies span almost the full range of SSFR values. We use the Spitzer Infrared Nearby Galaxy Survey (SINGS) to construct a comparison subsample of galaxies that (1) match HCG galaxies in J-band total galaxy luminosity and (2) are not strongly interacting and largely isolated. This selection eliminates mostly low-luminosity dwarfs and galaxies with some degree of peculiarity, providing a substantially improved, quiescent control sample. Unlike HCG galaxies, galaxies in the comparison SINGS subsample are continuously distributed both in SSFR and alpha-IRAC, although they show ranges in SFR(sub TOTAL) values, morphologies and stellar masses similar to those for HCG systems. We test the SSFR bimodality against a number of uncertainties, and find that these can only lead to its further enhancement. Excluding galaxies belonging to HCGs with three giant galaxies (triplets) leaves both the SSFR and the alpha-IRAC bimodality completely unaffected. We interpret these results as further evidence that an environment characterized by high galaxy number densities and low galaxy velocity dispersions, such as the one found in compact groups, plays a key role in accelerating galaxy evolution by enhancing star formation processes in galaxies and favoring a fast transition to quiescence.

Published
2010
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72. An X-ray + Radio Search for Massive Black Holes in Blue Compact Dwarf Galaxies

Author

Latimer, Colin J., Reines, Amy E., Plotkin, Richard M., Russell, Thomas D., Condon, James J., Latimer, Colin J., Reines, Amy E., Plotkin, Richard M., Russell, Thomas D., and Condon, James J.

Abstract

Nearby blue compact dwarf (BCD) galaxies are arguably our best local analogues of galaxies in the earlier Universe that may host relics of black hole (BH) seeds. Here we present high-resolution Chandra X-ray Observatory and Karl G. Jansky Very Large Array (VLA) observations of five nearby BCDs with stellar masses of less than the Small Magellanic Cloud ($M_\star \sim 10^{7} - 10^{8.4}$ $M_\odot$). We search for signatures of accreting massive BHs at X-ray and radio wavelengths, which are more sensitive to lower BH accretion rates than optical searches. We detect a total of 10 hard X-ray sources and 10 compact radio sources at luminosities consistent with star-formation-related emission. We find one case of a spatially-coincident X-ray and radio source within the astrometric uncertainties. If the X-ray and radio emission are indeed coming from the same source, the origin of the radiation is plausibly from an active massive BH with log $(M_{\rm BH}/M_{\odot}) \sim 4.8 \pm 1.1$. However, given that the X-ray and radio emission are also coincident with a young star cluster complex, we consider the combination of an X-ray binary and a supernova remnant (or \HII\ region) a viable alternative explanation. Overall, we do not find compelling evidence for active massive BHs in our target BCDs, which on average have stellar masses more than an order of magnitude lower than previous samples of dwarf galaxies found to host massive BHs. Our results suggest that moderately accreting massive BHs in BCDs are not so common as to permit unambiguous detection in a small sample., Comment: 13 pages, 4 figures, accepted for publication in ApJ

Published
2019
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80. Hard X-Ray-selected AGNs in Low-mass Galaxies from the NuSTAR Serendipitous Survey

Author

Chen (陳建廷), C.-T. J., primary, Brandt, W. N., additional, Reines, A. E., additional, Lansbury, G., additional, Stern, D., additional, Alexander, D. M., additional, Bauer, F., additional, Moro, A. Del, additional, Gandhi, P., additional, Harrison, F. A., additional, Hickox, R. C., additional, Koss, M. J., additional, Lanz, L., additional, Luo, B., additional, Mullaney, J. R., additional, Ricci, C., additional, and Trump, J. R., additional

Published
2017
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82. Giant black hole in a stripped galaxy

Author

Reines, Amy E.

Subjects
Black holes (Astronomy) -- Observations, Galaxies -- Observations, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

An oversized, supermassive black hole has been discovered at the centre of a densely packed conglomeration of stars. The finding suggests that the system is the stripped nucleus of a [...]

Published
2014

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