Browsing by Author "Alexander, D. M."

Now showing 1 - 20 of 33
  • Thumbnail Image
    Item
    A new population of compton-thick AGNs identified using the spectral curvature above 10 keV.
    (2016) Koss, M.; Bauer, Franz Erik; Ricci, Claudio; Treister, Ezequiel; Assef T., Roberto; Balokovic, M.; Stern, Daniel.; Gandhi, P.; Lamperti, I.; Alexander, D. M.
  • Thumbnail Image
    Item
    A new, faint population of X-ray transients.
    (2017) Bauer, Franz Erik; Treister, Ezequiel; Schulze, Steve.; Schawinski, Kevin; Luo, B.; Alexander, D. M.; Brandt, W N.; Comastri, A.; Forster, Francisco; Gilli, Roberto
  • Thumbnail Image
    Item
    A NuStar survey of nearby ultraluminous infrared galaxies
    (2015) Teng, Stacy H.; Rigby, Jane R.; Stern, Daniel; Ptak, Andrew; Alexander, D. M.; Bauer, Franz Erik; Boggs, Stephen E.; Brandt, W. Niel; Christensen, Finn E.; Comastri, Andrea
  • Thumbnail Image
    Item
    A NuSTAR survey of nearby ultraluminous infrared galaxies.
    (2015) Teng, Stacy H.; Bauer, Franz Erik; Treister, Ezequiel; Rigby, Jane R.; Stern, Daniel.; Ptak, Andrew.; Alexander, D. M.; Boggs, Stephen E.; Brandt, W N.; Christensen, Finn E.
  • Thumbnail Image
    Item
    An extragalactic spectroscopic survey of the SSA22 field
    (2015) Saez, C.; Lehmer, B. D.; Bauer, Franz Erik; Stern, D.; Gonzales, A.; Rreza, I.; Alexander, D. M.; Matsuda, Y.; Geach, J. E.; Harrison, F. A.
  • Thumbnail Image
    Item
    GOODS-ALMA 2.0: Source catalog, number counts, and prevailing compact sizes in 1.1 mm galaxies
    (2022) Gómez-Guijarro, C.; Elbaz, D.; Xiao, M.; Béthermin, M.; Franco, M.; Magnelli, B.; Daddi, E.; Dickinson, M.; Demarco, R.; Inami, H.; Rujopakarn, W.; Magdis, G. E.; Shu, X.; Chary, R.; Zhou, L.; Alexander, D. M.; Bournaud, F.; Ciesla, L.; Ferguson, H. C.; Finkelstein, S. L.; Giavalisco, M.; Iono, D.; Juneau, S.; Kartaltepe, J. S.; Lagache, G.; Le Floc'h, E.; Leiton, R.; Lin, L.; Motohara, K.; Mullaney, J.; Okumura, K.; Pannella, M.; Papovich, C.; Pope, A.; Sargent, M. T.; Silverman, J. D.; Treister, E.; Wang, T.
    Submillimeter/millimeter observations of dusty star-forming galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA) have shown that dust continuum emission generally occurs in compact regions smaller than the stellar distribution. However, it remains to be understood how systematic these findings are. Studies often lack homogeneity in the sample selection, target discontinuous areas with inhomogeneous sensitivities, and suffer from modest uv coverage coming from single array configurations. GOODS-ALMA is a 1.1 mm galaxy survey over a continuous area of 72.42 arcmin(2) at a homogeneous sensitivity. In this version 2.0, we present a new low resolution dataset and its combination with the previous high resolution dataset from the survey, improving the uv coverage and sensitivity reaching an average of sigma = 68.4 mu Jy beam(-1). A total of 88 galaxies are detected in a blind search (compared to 35 in the high resolution dataset alone), 50% at S/N-peak >= 5 and 50% at 3.5 <= S/N-peak <= 5 aided by priors. Among them, 13 out of the 88 are optically dark or faint sources (H- or K-band dropouts). The sample dust continuum sizes at 1.1 mm are generally compact, with a median effective radius of R-e = 0 ''.10 +/- 0 ''.5 (a physical size of R-e = 0.73 +/- 0.29 kpc at the redshift of each source). Dust continuum sizes evolve with redshift and stellar mass resembling the trends of the stellar sizes measured at optical wavelengths, albeit a lower normalization compared to those of late-type galaxies. We conclude that for sources with flux densities S-1.1mm > 1 mJy, compact dust continuum emission at 1.1 mm prevails, and sizes as extended as typical star-forming stellar disks are rare. The S-1.1mm < 1 mJy sources appear slightly more extended at 1.1 mm, although they are still generally compact below the sizes of typical star-forming stellar disks.
  • Thumbnail Image
    Item
    Hard X-Ray-selected AGNs in Low-mass Galaxies from the NuSTAR Serendipitous Survey
    (2017) Chen, C. T. J.; Brandt, W. N.; Reines, A. E.; Lansbury, G.; Stern, D.; Alexander, D. M.; Bauer, Franz Erik; Ricci, Claudio; Del Moro, A.; Gandhi, P.; Harrison, F. A.; Hickox, R. C.; Koss, M. J.; Lanz, L.; Koss, M. J.; Lanz, L.; Luo, B.; Ricci, Claudio
  • Thumbnail Image
    Item
    IC 3639—A NEW BONA FIDE COMPTON-THICK AGN UNVEILED BY NuSTAR
    (2016) Boorman, Peter G.; Gandhi, P.; Alexander, D. M.; Annuar, A.; Ballantyne, D. R.; Bauer, Franz Erik; Boggs, S. E.; Brandt, W. N.; Brightman, M.; Christensen, F. E.; Craig, W. W.; Farrah, D.; Hailey, C. J.; Harrison, F. A.; Hönig, S. F.; Koss, M.; LaMassa, S. M.; Masini, A. C.; Ricci, G.; Risaliti, D.; Stern, W.; Zhang, W.
  • Thumbnail Image
    Item
    LLAMA: normal star formation efficiencies of molecular gas in the centres of luminous Seyfert galaxies.
    (2018) Rosario, D.; Ricci, Claudio; Treister, Ezequiel; Burtscher, L.; Davies, R. I.; Koss, M.; Lutz, D.; Riffel, R.; Alexander, D. M.; Genzel, R.; Hicks, E. H.
  • Thumbnail Image
    Item
    NuSTAR J033202-2746.8: Direct Constraints on the Compton Reflection in a Heavily Obscured Quasar at z ≈ 2.
    (2014) Del Moro, A.; Bauer, Franz Erik; Treister, Ezequiel; Mullaney, J. R.; Alexander, D. M.; Comastri, A.; Stern, D.; Civano, F.; Ranalli, P.; Vignali, C.; Aird, J. A.
  • No Thumbnail Available
    Item
    NuSTAR observations of four nearby X-ray faint AGNs: low luminosity or heavy obscuration?
    (OUP, 2020) Annuar, A.; Alexander, D. M.; Gandhi, P.; Lansbury, G. B.; Asmus, D.; Balokovic, M.; Ballantyne, D. R.; Bauer, Franz Erik; Boorman, P. G.; Brandt, W. N.; Brightman, M.; Chen, C. T. J.; Del Moro, A.; Farrah, D.; Harrison, F. A.; Koss, M. J.; Lanz, L.; Marchesi, S.; Masini, A.; Nardini, E.; Ricci, Claudio; Stern, D.; Zappacosta, L.
    We present NuSTAR (Nuclear Spectroscopic Telescope Array) observations of four active galactic nuclei (AGNs) located within 15 Mpc. These AGNs, namely ESO 121-G6, NGC 660, NGC 3486, and NGC 5195, have observed X-ray luminosities of L 2–10 keV,obs ≲ 10 39 erg s −1 , classifying them as low-luminosity AGN (LLAGN). We perform broad-band X-ray spectral analysis for the AGN by combining our NuSTAR data with Chandra or XMM–Newton observations to directly measure their column densities (N H ) and infer their intrinsic power. We complement our X-ray data with archival and new high-angular resolution mid-infrared (mid-IR) data for all objects, except NGC 5195. Based on our X-ray spectral analysis, we found that both ESO 121-G6 and NGC 660 are heavily obscured (N H > 10 23 cm −2 ; L 2–10 keV,int ∼ 10 41 erg s −1 ), and NGC 660 may be Compton thick. We also note that the X-ray flux and spectral slope for ESO 121-G6 have significantly changed over the last decade, indicating significant changes in the obscuration and potentially accretion rate. On the other hand, NGC 3486 and NGC 5195 appear to be unobscured and just mildly obscured, respectively, with L 2–10 keV,int < 10 39 erg s −1 , i.e. genuine LLAGN. Both of the heavily obscured AGNs have L bol > 10 41 erg s −1 and λ Edd ≳ 10 −3 , and are detected in high-angular resolution mid-IR imaging, indicating the presence of obscuring dust on nuclear scale. NGC 3486, however, is undetected in high-resolution mid-IR imaging, and the current data do not provide stringent constraints on the presence or absence of obscuring nuclear dust in the AGN.
  • Thumbnail Image
    Item
    NuSTAR Observations of WISE J1036+0449, a Galaxy at z~1 Obscured by Hot Dust.
    (2017) Ricci, Claudio; Bauer, Franz Erik; Treister, Ezequiel; Nikutta, R.; Assef T., Roberto; Stern, D.; Alexander, D. M.; Asmus, D.; Ballantyne, D. R.; Blain, A. W.; Boggs, Steven E.
  • Thumbnail Image
    Item
    Obscured Active Galactic Nuclei and the X-Ray, Optical, and Far-Infrared Number Counts of Active Galactic Nuclei in the GOODS Fields.
    (2004) Treister, Ezequiel; Bauer, Franz Erik; Urry, C. Meg; Chatzichristou, Eleni; Alexander, D. M.; Koekemoer, Anton; Van Duyne, Jeffrey; Brandt, William N.; Bergeron, Jacqueline; Stern, Daniel; Moustakas, Leonidas A.
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Storm in a "teacup": a radio-quiet quasar with approximate to 10 kpc radio-emitting bubbles and extreme gas kinematics
    (2015) Harrison, C. M.; Thomson, A. P.; Alexander, D. M.; Bauer, Franz Erik; Edge, A. C.; Hogan, M. T.; Mullaney, J. R.; Swinbank, A. M.
  • Thumbnail Image
    Item
    The 2 Ms Chandra Deep Field-North Survey and the 250 ks Extended Chandra Deep Field-South Survey : Improved Point-Source Catalogs
    (2016) Xue, Y. Q.; Luo, B.; Brandt, W. N.; Alexander, D. M.; Bauer, Franz Erik; Lehmer, B. D.; Yang, G.
  • Thumbnail Image
    Item
    THE CHANDRA DEEP FIELD-SOUTH SURVEY: 7 MS SOURCE CATALOGS
    (2017) Luo, B.; Brandt, W. N.; Xue, Y. Q.; Lehmer, B.; Alexander, D. M.; Bauer, Franz Erik; Vito, F.; Yang, G.; Basu-Zych, A. R.; Comastri, A.
  • Thumbnail Image
    Item
    The fall of active galactic nuclei and the rise of star-forming galaxies : a close look at the chandra deep field X-ray number counts.
    (2004) Bauer, Franz Erik; Treister, Ezequiel; Alexander, D. M.; Brandt, W N.; Schneider, D. P.; Hornschemeier, A.E.; Garmire, G. P.
  • Thumbnail Image
    Item
    The hidden side of cosmic star formation at z > 3 Bridging optically dark and Lyman-break galaxies with GOODS-ALMA
    (Wiley, 2023) Xiao, M-Y.; Elbaz, D.; Gomez-Guijarro, C.; Leroy, L.; Bing, L-J.; Daddi, E.; Magnelli, B.; Franco, M.; Zhou, L.; Dickinson, M.; Wang, T.; Rujopakarn, W.; Magdis, G. E.; Treister, Ezequiel; Inami, H.; Demarco, R.; Sargent, M. T.; Shu, X.; Kartaltepe, J. S.; Alexander, D. M.; Bethermin, M.; Bournaud, F.; Ciesla, L.; Ferguson, H. C.; Finkelstein, S. L.; Giavalisco, M.; Gu, Q-S.; Iono, D.; Juneau, S.; Lagache, G.; Leiton, R.; Messias, H.; Motohara, K.; Mullaney, J.; Nagar, N.; Pannella, M.; Papovich, C.; Pope, A.; Schreiber, C.; Silverman, J.
    Our current understanding of the cosmic star formation history at z > 3 is primarily based on UV-selected galaxies (Lyman-break galaxies, i.e., LBGs). Recent studies of H-dropouts (HST-dark galaxies) have revealed that we may be missing a large proportion of star formation that is taking place in massive galaxies at z > 3. In this work, we extend the H-dropout criterion to lower masses to select optically dark or faint galaxies (OFGs) at high redshifts in order to complete the census between LBGs and H-dropouts. Our criterion (H > 26.5 mag & [4.5] < 25 mag) combined with a de-blending technique is designed to select not only extremely dust-obscured massive galaxies but also normal star-forming galaxies (typically E(B - V) > 0.4) with lower stellar masses at high redshifts. In addition, with this criterion, our sample is not contaminated by massive passive or old galaxies. In total, we identified 27 OFGs at (Zphot) > 3 (with a median of z(med) = 4.1) in the GOODS-ALMA field, covering a wide distribution of stellar masses with log(M-star/M-circle dot) = 9.4-11.1 (with a median of log(M-star med/M-circle dot) = 10.3). We find that up to 75% of the OFGs with log(M-star/M-circle dot) = 9.5-10.5 were neglected by previous LBGs and H-dropout selection techniques. After performing an optical-to-millimeter stacking analysis of the OFGs, we find that rather than being limited to a rare population of extreme starbursts, these OFGs represent a normal population of dusty star-forming galaxies at z > 3. The OFGs exhibit shorter gas depletion timescales, slightly lower gas fractions, and lower dust temperatures than the scaling relation of typical star-forming galaxies. Additionally, the total star formation rate (SFRtot = SFRIR + SFRUV) of the stacked OFGs is much higher than the SFRUVcorr (SFRUV corrected for dust extinction), with an average SFRtot/SFRUVcorr = 8 +/- 1, which lies above (similar to 0.3 dex) the 16-84th percentile range of typical star-forming galaxies at 3 <= z <= 6. All of the above suggests the presence of hidden dust regions in the OFGs that absorb all UV photons, which cannot be reproduced with dust extinction corrections. The effective radius of the average dust size measured by a circular Gaussian model fit in the uv plane is R-e(1.13 mm) = 1.01 +/- 0.05 kpc. After excluding the five LBGs in the OFG sample, we investigated their contributions to the cosmic star formation rate density (SFRD). We found that the SFRD at z > 3 contributed by massive OFGs (log(M-star/M-circle dot) > 10.3) is at least two orders of magnitude higher than the one contributed by equivalently massive LBGs. Finally, we calculated the combined contribution of OFGs and LBGs to the cosmic SFRD at z = 4-5 to be 4 x 10(-2) M-circle dot yr(-1) Mpc(-3), which is about 0.15 dex (43%) higher than the SFRD derived from UV-selected samples alone at the same redshift. This value could be even larger, as our calculations were performed in a very conservative way.
  • Thumbnail Image
    Item
    The hidden side of cosmic star formation at z > 3 Bridging optically dark and Lyman-break galaxies with GOODS-ALMA
    (2023) Xiao, M-Y.; Elbaz, D.; Gomez-Guijarro, C.; Leroy, L.; Bing, L-J.; Daddi, E.; Magnelli, B.; Franco, M.; Zhou, L.; Dickinson, M.; Wang, T.; Rujopakarn, W.; Magdis, G. E.; Treister, Ezequiel; Inami, H.; Demarco, R.; Sargent, M. T.; Shu, X.; Kartaltepe, J. S.; Alexander, D. M.; Bethermin, M.; Bournaud, F.; Ciesla, L.; Ferguson, H. C.; Finkelstein, S. L.; Giavalisco, M.; Gu, Q-S.; Iono, D.; Juneau, S.; Lagache, G.; Leiton, R.; Messias, H.; Motohara, K.; Mullaney, J.; Nagar, N.; Pannella, M.; Papovich, C.; Pope, A.; Schreiber, C.; Silverman, J.
    Our current understanding of the cosmic star formation history at z > 3 is primarily based on UV-selected galaxies (Lyman-break galaxies, i.e., LBGs). Recent studies of H-dropouts (HST-dark galaxies) have revealed that we may be missing a large proportion of star formation that is taking place in massive galaxies at z > 3. In this work, we extend the H-dropout criterion to lower masses to select optically dark or faint galaxies (OFGs) at high redshifts in order to complete the census between LBGs and H-dropouts. Our criterion (H > 26.5 mag & [4.5] < 25 mag) combined with a de-blending technique is designed to select not only extremely dust-obscured massive galaxies but also normal star-forming galaxies (typically E(B - V) > 0.4) with lower stellar masses at high redshifts. In addition, with this criterion, our sample is not contaminated by massive passive or old galaxies. In total, we identified 27 OFGs at (Zphot) > 3 (with a median of z(med) = 4.1) in the GOODS-ALMA field, covering a wide distribution of stellar masses with log(M-star/M-circle dot) = 9.4-11.1 (with a median of log(M-star med/M-circle dot) = 10.3). We find that up to 75% of the OFGs with log(M-star/M-circle dot) = 9.5-10.5 were neglected by previous LBGs and H-dropout selection techniques. After performing an optical-to-millimeter stacking analysis of the OFGs, we find that rather than being limited to a rare population of extreme starbursts, these OFGs represent a normal population of dusty star-forming galaxies at z > 3. The OFGs exhibit shorter gas depletion timescales, slightly lower gas fractions, and lower dust temperatures than the scaling relation of typical star-forming galaxies. Additionally, the total star formation rate (SFRtot = SFRIR + SFRUV) of the stacked OFGs is much higher than the SFRUVcorr (SFRUV corrected for dust extinction), with an average SFRtot/SFRUVcorr = 8 +/- 1, which lies above (similar to 0.3 dex) the 16-84th percentile range of typical star-forming galaxies at 3 <= z <= 6. All of the above suggests the presence of hidden dust regions in the OFGs that absorb all UV photons, which cannot be reproduced with dust extinction corrections. The effective radius of the average dust size measured by a circular Gaussian model fit in the uv plane is R-e(1.13 mm) = 1.01 +/- 0.05 kpc. After excluding the five LBGs in the OFG sample, we investigated their contributions to the cosmic star formation rate density (SFRD). We found that the SFRD at z > 3 contributed by massive OFGs (log(M-star/M-circle dot) > 10.3) is at least two orders of magnitude higher than the one contributed by equivalently massive LBGs. Finally, we calculated the combined contribution of OFGs and LBGs to the cosmic SFRD at z = 4-5 to be 4 x 10(-2) M-circle dot yr(-1) Mpc(-3), which is about 0.15 dex (43%) higher than the SFRD derived from UV-selected samples alone at the same redshift. This value could be even larger, as our calculations were performed in a very conservative way.