DSpace Angular :: Browsing by Author "Koekemoer, Anton M."

Browsing by Author "Koekemoer, Anton M."

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A Transient "Changing-look" Active Galactic Nucleus Resolved on Month Timescales from First-year Sloan Digital Sky Survey V Data
(2022) Zeltyn, Grisha; Trakhtenbrot, Benny; Eracleous, Michael; Runnoe, Jessie; Trump, Jonathan R.; Stern, Jonathan; Shen, Yue; Hernandez-Garcia, Lorena; Bauer, Franz E.; Yang, Qian; Dwelly, Tom; Ricci, Claudio; Green, Paul; Anderson, Scott F.; Assef, Roberto J.; Guolo, Muryel; MacLeod, Chelsea; Davis, Megan C.; Fries, Logan; Gezari, Suvi; Grogin, Norman A.; Homan, David; Koekemoer, Anton M.; Krumpe, Mirko; LaMassa, Stephanie; Liu, Xin; Merloni, Andrea; Martinez-Aldama, Mary Loli; Schneider, Donald P.; Temple, Matthew J.; Brownstein, Joel R.; Ibarra-Medel, Hector; Burke, Jamison; Pellegrino, Craig; Kollmeier, Juna A.
We report the discovery of a new "changing-look" active galactic nucleus (CLAGN) event, in the quasar SDSS J162829.17+432948.5 at z = 0.2603, identified through repeat spectroscopy from the fifth Sloan Digital Sky Survey (SDSS-V). Optical photometry taken during 2020-2021 shows a dramatic dimming of Delta g approximate to 1 mag, followed by a rapid recovery on a timescale of several months, with the less than or similar to 2 month period of rebrightening captured in new SDSS-V and Las Cumbres Observatory spectroscopy. This is one of the fastest CLAGN transitions observed to date. Archival observations suggest that the object experienced a much more gradual dimming over the period of 2011-2013. Our spectroscopy shows that the photometric changes were accompanied by dramatic variations in the quasar-like continuum and broad-line emission. The excellent agreement between the pre- and postdip photometric and spectroscopic appearances of the source, as well as the fact that the dimmest spectra can be reproduced by applying a single extinction law to the brighter spectral states, favor a variable line-of-sight obscuration as the driver of the observed transitions. Such an interpretation faces several theoretical challenges, and thus an alternative accretion-driven scenario cannot be excluded. The recent events observed in this quasar highlight the importance of spectroscopic monitoring of large active galactic nucleus samples on weeks-to-months timescales, which the SDSS-V is designed to achieve.
A variable active galactic nucleus at z=2.06 triply-imaged by the galaxy cluster MACS J0035.4-2015
(2023) Furtak, Lukas J.; Mainali, Ramesh; Zitrin, Adi; Plat, Adele; Fujimoto, Seiji; Donahue, Megan; Nelson, Erica J.; Bauer, Franz E.; Uematsu, Ryosuke; Caminha, Gabriel B.; Andrade-Santos, Felipe; Bradley, Larry D.; Caputi, Karina, I; Charlot, Stephane; Chevallard, Jacopo; Coe, Dan; Curtis-Lake, Emma; Espada, Daniel; Frye, Brenda L.; Knudsen, Kirsten K.; Koekemoer, Anton M.; Kohno, Kotaro; Kokorev, Vasily; Laporte, Nicolas; Lee, Minju M.; Lemaux, Brian C.; Magdis, Georgios E.; Sharon, Keren; Stark, Daniel P.; Su, Yuanyuan; Suess, Katherine A.; Ueda, Yoshihiro; Umehata, Hideki; Vidal-Garcia, Alba; Wu, John F.
We report the discovery of a triply imaged active galactic nucleus (AGN), lensed by the galaxy cluster MACS J0035.4-2015 (z(d) = 0.352). The object is detected in Hubble Space Telescope imaging taken for the RELICS program. It appears to have a quasi-stellar nucleus consistent with a point-source, with a de-magnified radius of r(e) less than or similar to 100 pc. The object is spectroscopically confirmed to be an AGN at z spec = 2.063 +/- 0.005 showing broad rest-frame UV emission lines, and detected in both X-ray observations with Chandra and in ALCS ALMA band 6 (1.2 mm) imaging. It has a relatively faint rest-frame UV luminosity for a quasar-like object, M (UV, 1450) = -19.7 +/- 0.2. The object adds to just a few quasars or other X-ray sources known to be multiply lensed by a galaxy cluster. Some diffuse emission from the host galaxy is faintly seen around the nucleus, and there is a faint object nearby sharing the same multiple-imaging symmetry and geometric redshift, possibly an interacting galaxy or a star-forming knot in the host. We present an accompanying lens model, calculate the magnifications and time delays, and infer the physical properties of the source. We find the rest-frame UV continuum and emission lines to be dominated by the AGN, and the optical emission to be dominated by the host galaxy of modest stellar mass M-* similar or equal to 10(9.2) M-circle dot. We also observe some variation in the AGN emission with time, which may suggest that the AGN used to be more active. This object adds a low-redshift counterpart to several relatively faint AGN recently uncovered at high redshifts with HST and JWST.
ALMA Lensing Cluster Survey: Full Spectral Energy Distribution Analysis of z ∼ 0.5-6 Lensed Galaxies Detected with millimeter Observations
(2024) Uematsu, Ryosuke; Ueda, Yoshihiro; Kohno, Kotaro; Toba, Yoshiki; Yamada, Satoshi; Smail, Ian; Umehata, Hideki; Fujimoto, Seiji; Hatsukade, Bunyo; Ao, Yiping; Bauer, Franz Erik; Brammer, Gabriel; Dessauges-Zavadsky, Miroslava; Espada, Daniel; Jolly, Jean-Baptiste; Koekemoer, Anton M.; Kokorev, Vasily; Magdis, Georgios E.; Oguri, Masamune; Sun, Fengwu
Sub/millimeter galaxies are a key population for the study of galaxy evolution because the majority of star formation at high redshifts occurred in galaxies deeply embedded in dust. To search for this population, we have performed an extensive survey with Atacama Large Millimeter/submillimeter Array (ALMA), called the ALMA Lensing Cluster Survey (ALCS). This survey covers 133 arcmin(2) area and securely detects 180 sources at z similar to 0.5-6 with a flux limit of similar to 0.2 mJy at 1.2 mm. Here, we report the results of multiwavelength spectral energy distribution analysis of the whole ALCS sample, utilizing the observed-frame UV to millimeter photometry. We find that the majority of the ALCS sources lie on the star-forming main sequence, with a smaller fraction showing intense starburst activities. The ALCS sample contains high infrared-excess sources ( IRX = log ( L dust / L UV ) > 1 ), including two extremely dust-obscured galaxies (IRX > 5). We also confirm that the ALCS sample probes a broader range in lower dust mass than conventional submillimeter galaxy samples in the same redshift range. We identify six heavily obscured active galactic nucleus (AGN) candidates that are not detected in the archival Chandra data in addition to the three X-ray AGNs reported by Uematsu et al. (2023). The inferred AGN luminosity density shows a possible excess at z = 2-3 compared with that determined from X-ray surveys below 10 keV.
Characterization of Two 2 mm detected Optically Obscured Dusty Star-forming Galaxies
(2022) Manning, Sinclaire M.; Casey, Caitlin M.; Zavala, Jorge A.; Magdis, Georgios E.; Drew, Patrick M.; Champagne, Jaclyn B.; Aravena, Manuel; Béthermin, Matthieu; Clements, David L.; Finkelstein, Steven L.; Fujimoto, Seiji; Hayward, Christopher C.; Hodge, Jacqueline A.; Ilbert, Olivier; Kartaltepe, Jeyhan S.; Knudsen, Kirsten K.; Koekemoer, Anton M.; Man, Allison W. S.; Sanders, David B.; Sheth, Kartik; Spilker, Justin S.; Staguhn, Johannes; Talia, Margherita; Treister, Ezequiel; Yun, Min S.
The 2 mm Mapping Obscuration to Reionization with ALMA (MORA) Survey was designed to detect high-redshift (z greater than or similar to 4), massive, dusty star-forming galaxies (DSFGs). Here we present two likely high-redshift sources, identified in the survey, whose physical characteristics are consistent with a class of optical/near-infrared (OIR)-invisible DSFGs found elsewhere in the literature. We first perform a rigorous analysis of all available photometric data to fit spectral energy distributions and estimate redshifts before deriving physical properties based on our findings. Our results suggest the two galaxies, called MORA-5 and MORA-9, represent two extremes of the "OIR-dark" class of DSFGs. MORA-5 (z(phot) = 4.3(-1.3)(+1.5)) is a significantly more active starburst with a star formation rate (SFR) of 830(-190)(+340) M-circle dot yr(-1) compared to MORA-9 (z(phot) = 4.3(-1.0)(+1.3)), whose SFR is a modest 200(-60)(+250) M-circle dot yr(-1). Based on the stellar masses (M-star approximate to 10(10-11) M-circle dot), space density (n similar to (5 +/- 2) x 10(-6) Mpc(-3), which incorporates two other spectroscopically confirmed OIR-dark DSFGs in the MORA sample at z = 4.6 and z = 5.9), and gas depletion timescales (<1 Gyr) of these sources, we find evidence supporting the theory that OIR-dark DSFGs are the progenitors of recently discovered 3 < z < 4 massive quiescent galaxies.
Exploring Changing-look Active Galactic Nuclei with the Sloan Digital Sky Survey V: First Year Results
(2024) Zeltyn, Grisha; Trakhtenbrot, Benny; Eracleous, Michael; Yang, Qian; Green, Paul; Anderson, Scott F.; LaMassa, Stephanie; Runnoe, Jessie; Assef, Roberto J.; Bauer, Franz E.; Brandt, W. N.; Davis, Megan C.; Frederick, Sara E.; Fries, Logan B.; Graham, Matthew J.; Grogin, Norman A.; Guolo, Muryel; Hernandez-Garcia, Lorena; Koekemoer, Anton M.; Krumpe, Mirko; Liu, Xin; Martinez-Aldama, Mary Loli; Ricci, Claudio; Schneider, Donald P.; Shen, Yue; Sniegowska, Marzena; Temple, Matthew J.; Trump, Jonathan R.; Xue, Yongquan; Brownstein, Joel R.; Dwelly, Tom; Morrison, Sean; Bizyaev, Dmitry; Pan, Kaike; Kollmeier, Juna A.
"Changing-look" active galactic nuclei (CL-AGNs) challenge our basic ideas about the physics of accretion flows and circumnuclear gas around supermassive black holes. Using first-year Sloan Digital Sky Survey V (SDSS-V) repeated spectroscopy of nearly 29,000 previously known active galactic nuclei (AGNs), combined with dedicated follow-up spectroscopy, and publicly available optical light curves, we have identified 116 CL-AGNs where (at least) one broad emission line has essentially (dis-)appeared, as well as 88 other extremely variable systems. Our CL-AGN sample, with 107 newly identified cases, is the largest reported to date, and includes similar to 0.4% of the AGNs reobserved in first-year SDSS-V operations. Among our CL-AGNs, 67% exhibit dimming while 33% exhibit brightening. Our sample probes extreme AGN spectral variability on months to decades timescales, including some cases of recurring transitions on surprisingly short timescales (less than or similar to 2 months in the rest frame). We find that CL events are preferentially found in lower-Eddington-ratio (f Edd) systems: Our CL-AGNs have a f Edd distribution that significantly differs from that of a carefully constructed, redshift- and luminosity-matched control sample (Anderson-Darling test yielding p AD approximate to 6 x 10-5; median f Edd approximate to 0.025 versus 0.043). This preference for low f Edd strengthens previous findings of higher CL-AGN incidence at lower f Edd, found in smaller samples. Finally, we show that the broad Mg ii emission line in our CL-AGN sample tends to vary significantly less than the broad H beta emission line. Our large CL-AGN sample demonstrates the advantages and challenges in using multi-epoch spectroscopy from large surveys to study extreme AGN variability and physics.
Extensive Lensing Survey of Optical and Near-infrared Dark Objects (El Sonido): HST H-faint Galaxies behind 101 Lensing Clusters
(2021) Sun, Fengwu; Egami, Eiichi; Perez-Gonzalez, Pablo G.; Smail, Ian; Caputi, Karina I.; Bauer, Franz E.; Rawle, Timothy D.; Fujimoto, Seiji; Kohno, Kotaro; Dudzeviciute, Ugne; Atek, Hakim; Bianconi, Matteo; Chapman, Scott C.; Combes, Francoise; Jauzac, Mathilde; Jolly, Jean-Baptiste; Koekemoer, Anton M.; Magdis, Georgios E.; Rodighiero, Giulia; Rujopakarn, Wiphu; Schaerer, Daniel; Steinhardt, Charles L.; Van der Werf, Paul; Walth, Gregory L.; Weaver, John R.
We present a Spitzer/IRAC survey of H-faint (H-160 greater than or similar to 26.4, < 5 sigma) sources in 101 lensing cluster fields. Across a CANDELS/Wide-like survey area of similar to 648 arcmin(2) (effectively similar to 221 arcmin(2) in the source plane), we have securely discovered 53 sources in the IRAC Channel-2 band (CH2, 4.5 mu m; median CH2 = 22.46 +/- 0.11 AB mag) that lack robust HST/WFC3-IR F160W counterparts. The most remarkable source in our sample, namely ES-009 in the field of Abell 2813, is the brightest H-faint galaxy at 4.5 mu m known so far (CH2 = 20.48 +/- 0.03 AB mag). We show that the H-faint sources in our sample are massive (median M-star = 10 10.3 +/- 0.3 M-circle dot, star-forming (median star formation rate =1001 M-circle dot yr(-1)), and dust-obscured (A(v) = 2.6 +/- 0.3) galaxies around a median photometric redshift of z = 3.9 +/- 0.4. The stellar continua of 14 H-faint galaxies can be resolved in the CH2 band, suggesting a median circularized effective radius (R-e,R-circ; lensing corrected) of 1.9 +/- 0.2 kpc and <1.5 kpc for the resolved and whole samples, respectively. This is consistent with the sizes of massive unobscured galaxies at z similar to 4, indicating that H-faint galaxies represent the dusty tail of the distribution of a wider galaxy population. Comparing with the ALMA dust continuum sizes of similar galaxies reported previously, we conclude that the heavy dust obscuration in H-faint galaxies is related to the compactness of both stellar and dust continua (R-e,R-circ similar to 1 kpc). These H-faint galaxies make up 161 3 % of the galaxies in the stellar-mass range of 10(10) - 10(11.2) M-circle dot at z = 3 similar to 5, contributing to 8(-4)(+8)% of the cosmic star formation rate density in this epoch and likely tracing the early phase of massive galaxy formation.
Heavily Obscured AGN in Star-Forming Galaxies at z sime 2.
(2009) Treister, Ezequiel; Cardamone, Carolin N.; Schawinski, Kevin; Urry, C. Meg; Gawiser, Eric.; Virani, Shanil; Lira, Paulina; Kartaltepe, Jeyhan; Damen, Maaike; Taylor, EN.; Le Floc'H e; Justham, Stephen; Koekemoer, Anton M.
High-quality Extragalactic Legacy-field Monitoring (HELM) with DECam: Project Overview and First Data Release
(2024) Zhuang, Ming-Yang; Yang, Qian; Shen, Yue; Adamow, Monika; Friedel, Douglas N.; Gruendl, R. A.; Stone, Zachary; Li, Junyao; Liu, Xin; Martini, Paul; Abbott, Timothy M. C.; Anderson, Scott F.; Assef, Roberto J.; Bauer, Franz E.; Bielby, Richard; Brandt, W. N.; Burke, Colin J.; Casares, Jorge; Chen, Yu-Ching; De Rosa, Gisella; Drlica-Wagner, Alex; Dwelly, Tom; Eltvedt, Alice; Alvarez, Gloria Fonseca; Fu, Jianyang; Fuentes, Cesar; Graham, Melissa L.; Grier, Catherine J.; Golovich, Nathan; Hall, Patrick B.; Hartigan, Patrick; Horne, Keith; Koekemoer, Anton M.; Krumpe, Mirko; Li, Jennifer I.; Lidman, Chris; Malik, Umang; Mangian, Amelia; Merloni, Andrea; Ricci, Claudio; Salvato, Mara; Sharp, Rob; Trilling, David E.; Tucker, Brad E.; Wen, Di; Wideman, Zachary; Xue, Yongquan; Yu, Zhefu; Zucker, Catherine
High-quality Extragalactic Legacy-field Monitoring (HELM) is a long-term observing program that photometrically monitors several well-studied extragalactic legacy fields with the Dark Energy Camera (DECam) imager on the CTIO 4 m Blanco telescope. Since 2019 February, HELM has been monitoring regions within COSMOS, XMM-LSS, CDF-S, S-CVZ, ELAIS-S1, and SDSS Stripe 82 with few-day cadences in the (u)gri(z) bands, over a collective sky area of similar to 38 deg2. The main science goal of HELM is to provide high-quality optical light curves for a large sample of active galactic nuclei (AGNs), and to build decades-long time baselines when combining past and future optical light curves in these legacy fields. These optical images and light curves will facilitate the measurements of AGN reverberation mapping lags, as well as studies of AGN variability and its dependencies on accretion properties. In addition, the time-resolved and coadded DECam photometry will enable a broad range of science applications from galaxy evolution to time-domain science. We describe the design and implementation of the program and present the first data release that includes source catalogs and the first similar to 3.5 yr of light curves during 2019A-2022A.
Investigating the Effect of Galaxy Interactions on Star Formation at 0.5 < z < 3.0
(2022) Shah, Ekta A.; Kartaltepe, Jeyhan S.; Magagnoli, Christina T.; Cox, Isabella G.; Wetherell, Caleb T.; Vanderhoof, Brittany N.; Cooke, Kevin C.; Calabro, Antonello; Chartab, Nima; Conselice, Christopher J.; Croton, Darren J.; de la Vega, Alexander; Hathi, Nimish P.; Ilbert, Olivier; Inami, Hanae; Kocevski, Dale D.; Koekemoer, Anton M.; Lemaux, Brian C.; Lubin, Lori; Mantha, Kameswara Bharadwaj; Marchesi, Stefano; Martig, Marie; Moreno, Jorge; Pampliega, Belen Alcalde; Patton, David R.; Salvato, Mara; Treister, Ezequiel
Observations and simulations of interacting galaxies and mergers in the local universe have shown that interactions can significantly enhance the star formation rates (SFRs) and fueling of active galactic nuclei (AGN). However, at higher redshift, some simulations suggest that the level of star formation enhancement induced by interactions is lower due to the higher gas fractions and already increased SFRs in these galaxies. To test this, we measure the SFR enhancement in a total of 2351 (1327) massive (M* > 10(10)M(?)) major (1 < M-1/M-2 < 4) spectroscopic galaxy pairs at 0.5 < z < 3.0 with delta V < 5000 km s-1 (1000 km s(-1)) and projected separation < 150 kpc selected from the extensive spectroscopic coverage in the COSMOS and CANDELS fields. We find that the highest level of SFR enhancement is a factor of 1.23 (-0.09) (+0.08) in the closest projected separation bin (< 25 kpc) relative to a stellar mass-, redshift-, and environment-matched control sample of isolated galaxies. We find that the level of SFR enhancement is a factor of similar to 1.5 higher at 0.5 < z < 1 than at 1 < z < 3 in the closest projected separation bin. Among a sample of visually identified mergers, we find an enhancement of a factor of 1.86 (-0.18) (+0.29) (similar to 3 sigma) for coalesced systems. For this visually identified sample, we see a clear trend of increased SFR enhancement with decreasing projected separation (2.40-+0.62versus + 0.37 1.58(-0.20) (+0.29) for 0.5 < z < 1.6 and 1.6 < z < 3.0, respectively). The SFR enhancements seen in our interactions and mergers are all lower than the level seen in local samples at the same separation, suggesting that the level of interaction-induced star formation evolves significantly over this time period.
Pilot-WINGS: An extended MUSE view of the structure of Abell 370
(2022) Lagattuta, David J.; Richard, Johan; Bauer, Franz Erik; Cerny, Catherine; Claeyssens, Adelaide; Guaita, Lucia; Jauzac, Mathilde; Jeanneau, Alexandre; Koekemoer, Anton M.; Mahler, Guillaume; Prieto Lyon, Gonzalo; Acebron, Ana; Meneghetti, Massimo; Niemiec, Anna; Zitrin, Adi; Bianconi, Matteo; Connor, Thomas; Cen, Renyue; Edge, Alastair; Faisst, Andreas L.; Limousin, Marceau; Massey, Richard; Sereno, Mauro; Sharon, Keren; Weaver, John R.
We investigate the strong-lensing cluster Abell 370 (A370) using a wide Integral Field Unit (IFU) spectroscopic mosaic from the Multi-Unit Spectroscopic Explorer (MUSE). IFU spectroscopy provides significant insight into the structure and mass content of galaxy clusters, yet IFU-based cluster studies focus almost exclusively on the central Einstein-radius region. Covering over 14 arcmin(2), the new MUSE mosaic extends significantly beyond the A370 Einstein radius, providing, for the first time, a detailed look at the cluster outskirts. Combining these data with wide-field, multi-band Hubble Space Telescope (HST) imaging from the BUFFALO project, we analyse the distribution of objects within the cluster and along the line of sight. Identifying 416 cluster galaxies, we use kinematics to trace the radial mass profile of the halo, providing a mass estimate independent from the lens model. We also measure radially averaged properties of the cluster members, tracking their evolution as a function of infall. Thanks to the high spatial resolution of our data, we identify six cluster members acting as galaxy-galaxy lenses, which constrain localized mass distributions beyond the Einstein radius. Finally, taking advantage of MUSE's 3D capabilities, we detect and analyse multiple spatially extended overdensities outside of the cluster that influence lensing-derived halo mass estimates. We stress that much of this work is only possible thanks to the robust, extended IFU coverage, highlighting its importance even in less optically dense cluster regions. Overall, this work showcases the power of combining HST + MUSE, and serves as the initial step towards a larger and wider program targeting several clusters.

Browsing by Author "Koekemoer, Anton M."

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