ORCID Profile
0000-0001-9208-2143
Current Organisations
Harvard-Smithsonian Center for Astrophysics
,
Smithsonian Astrophysical Observatory
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Astronomical and Space Sciences | Galactic Astronomy | Cosmology and Extragalactic Astronomy
Expanding Knowledge in the Physical Sciences | Scientific Instruments | Electronic Information Storage and Retrieval Services |
Publisher: American Astronomical Society
Date: 09-01-2017
Publisher: American Astronomical Society
Date: 19-12-2018
Publisher: American Astronomical Society
Date: 22-07-2008
DOI: 10.1086/591422
Publisher: American Astronomical Society
Date: 08-02-2018
Publisher: American Astronomical Society
Date: 20-12-2003
DOI: 10.1086/379804
Publisher: EDP Sciences
Date: 05-2004
Publisher: Springer Science and Business Media LLC
Date: 04-2017
DOI: 10.1038/NATURE21680
Abstract: Finding massive galaxies that stopped forming stars in the early Universe presents an observational challenge because their rest-frame ultraviolet emission is negligible and they can only be reliably identified by extremely deep near-infrared surveys. These surveys have revealed the presence of massive, quiescent early-type galaxies appearing as early as redshift z ≈ 2, an epoch three billion years after the Big Bang. Their age and formation processes have now been explained by an improved generation of galaxy-formation models, in which they form rapidly at z ≈ 3-4, consistent with the typical masses and ages derived from their observations. Deeper surveys have reported evidence for populations of massive, quiescent galaxies at even higher redshifts and earlier times, using coarsely s led photometry. However, these early, massive, quiescent galaxies are not predicted by the latest generation of theoretical models. Here we report the spectroscopic confirmation of one such galaxy at redshift z = 3.717, with a stellar mass of 1.7 × 10
Publisher: American Astronomical Society
Date: 31-08-2022
Abstract: The discovery in deep near-infrared surveys of a population of massive quiescent galaxies at z 3 has given rise to the question of how they came to be quenched so early in the history of the universe. Measuring their molecular gas properties can distinguish between physical processes where they stop forming stars due to a lack of fuel versus those where the star formation efficiency is reduced and the gas is retained. We conducted Atacama Large Millimeter/submillimeter Array observations of four quiescent galaxies at z = 3.5–4.0 found by the Fourstar Galaxy Evolution Survey and a serendipitous optically dark galaxy at z = 3.71. We aim to investigate the presence of dust-obscured star formation and their gas content by observing the dust continuum emission at Band 7 and the atomic carbon [C i ]( 3 P 1 – 3 P 0 ) line at 492.16 GHz. Among the four quiescent galaxies, only one source is detected in the dust continuum at λ obs = 870 μ m. The submillimeter observations confirm their passive nature, and all of them are located more than four times below the main sequence of star-forming galaxies at z = 3.7. None of the targets are detected in [C i ], constraining their gas-mass fractions to be %. These gas-mass fractions are more than 3 times lower than the scaling relation for star-forming galaxies at z = 3.7. These results support scenarios where massive galaxies at z = 3.5–4.0 quench by consuming/expelling all the gas rather than by reducing the efficiency of the conversion of their gas into stars.
Publisher: American Astronomical Society
Date: 05-01-2017
Publisher: American Astronomical Society
Date: 24-03-2017
Publisher: American Astronomical Society
Date: 06-07-2010
Publisher: Oxford University Press (OUP)
Date: 14-03-2017
DOI: 10.1093/MNRAS/STX605
Publisher: American Astronomical Society
Date: 09-1999
DOI: 10.1086/307624
Publisher: American Astronomical Society
Date: 17-08-2018
Publisher: American Astronomical Society
Date: 26-09-2022
Abstract: We present spectroscopic confirmation of candidate strong gravitational lenses using the Keck Observatory and Very Large Telescope as part of our ASTRO 3D Galaxy Evolution with Lenses ( AGEL ) survey. We confirm that (1) search methods using convolutional neural networks (CNNs) with visual inspection successfully identify strong gravitational lenses and (2) the lenses are at higher redshifts relative to existing surveys due to the combination of deeper and higher-resolution imaging from DECam and spectroscopy spanning optical to near-infrared wavelengths. We measure 104 redshifts in 77 systems selected from a catalog in the DES and DECaLS imaging fields ( r ≤ 22 mag). Combining our results with published redshifts, we present redshifts for 68 lenses and establish that CNN-based searches are highly effective for use in future imaging surveys with a success rate of at least 88% (defined as 68/77). We report 53 strong lenses with spectroscopic redshifts for both the deflector and source ( z src z defl ), and 15 lenses with a spectroscopic redshift for either the deflector ( z defl 0.21) or source ( z src ≥ 1.34). For the 68 lenses, the deflectors and sources have average redshifts and standard deviations of 0.58 ± 0.14 and 1.92 ± 0.59 respectively, and corresponding redshift ranges of z defl = 0.21–0.89 and z src = 0.88–3.55. The AGEL systems include 41 deflectors at z defl ≥ 0.5 that are ideal for follow-up studies to track how mass density profiles evolve with redshift. Our goal with AGEL is to spectroscopically confirm ∼100 strong gravitational lenses that can be observed from both hemispheres throughout the year. The AGEL survey is a resource for refining automated all-sky searches and addressing a range of questions in astrophysics and cosmology.
Publisher: American Astronomical Society
Date: 30-09-2019
Publisher: American Astronomical Society
Date: 02-08-2018
Publisher: American Astronomical Society
Date: 09-04-2020
Publisher: American Astronomical Society
Date: 03-10-2017
Publisher: American Astronomical Society
Date: 22-02-2011
Publisher: Oxford University Press (OUP)
Date: 09-10-2018
Publisher: American Astronomical Society
Date: 10-10-2016
Publisher: American Astronomical Society
Date: 03-05-2018
Publisher: American Astronomical Society
Date: 12-03-2012
Publisher: AIP
Date: 2009
DOI: 10.1063/1.3293038
Publisher: American Astronomical Society
Date: 05-08-2013
Publisher: American Astronomical Society
Date: 21-07-2016
Publisher: American Astronomical Society
Date: 13-11-2013
Publisher: American Astronomical Society
Date: 26-10-2017
Publisher: EDP Sciences
Date: 2012
Publisher: American Astronomical Society
Date: 20-07-2007
DOI: 10.1086/518766
Publisher: American Astronomical Society
Date: 19-01-2016
Publisher: American Astronomical Society
Date: 09-09-2008
DOI: 10.1086/592730
Publisher: American Astronomical Society
Date: 08-06-2016
Publisher: American Astronomical Society
Date: 03-11-2018
Abstract: Deep near-infrared photometric surveys are efficient in identifying high-redshift galaxies, however, they can be prone to systematic errors in photometric redshift. This is particularly salient when there is limited s ling of key spectral features of a galaxy’s spectral energy distribution (SED), such as for quiescent galaxies where the expected age-sensitive Balmer/4000 Å break enters the K -band at z 4. With single-filter s ling of this spectral feature, degeneracies between SED models and redshift emerge. A potential solution to this comes from splitting the K band into multiple filters. We use simulations to show an optimal solution is to add two medium-band filters, K blue ( λ cen = 2.06 μ m, Δ λ = 0.25 μ m) and K red ( λ cen = 2.31 μ m, Δ λ = 0.27 μ m), that are complementary to the existing K s filter. We test the impact of the K -band filters with simulated catalogs comprised of galaxies with varying ages and signal-to-noise. The results suggest that the K -band filters do improve photometric redshift constraints on z 4 quiescent galaxies, increasing precision and reducing outliers by up to 90%. We find that the impact from the K -band filters depends on the signal-to-noise, the redshift, and the SED of the galaxy. The filters we designed were built and used to conduct a pilot of the FLAMINGOS-2 Extragalactic Near-Infrared K -band Split survey. While no new z 4 quiescent galaxies are identified in the limited area pilot, the K blue and K red filters indicate strong Balmer/4000 Å breaks in existing candidates. Additionally, we identify galaxies with strong nebular emission lines, for which the K -band filters increase photometric redshift precision and in some cases indicate extreme star formation.
Publisher: Oxford University Press (OUP)
Date: 25-11-0088
Publisher: American Astronomical Society
Date: 07-04-2005
DOI: 10.1086/430518
Publisher: American Astronomical Society
Date: 12-10-2015
Publisher: American Astronomical Society
Date: 03-2001
DOI: 10.1086/319085
Publisher: American Astronomical Society
Date: 02-02-2021
Publisher: American Astronomical Society
Date: 10-06-2006
DOI: 10.1086/503539
Publisher: American Astronomical Society
Date: 30-01-2017
Publisher: American Astronomical Society
Date: 18-04-2012
Publisher: Springer Science and Business Media LLC
Date: 19-12-2016
Publisher: American Astronomical Society
Date: 20-01-2005
DOI: 10.1086/426427
Publisher: American Astronomical Society
Date: 06-08-2004
DOI: 10.1086/424801
Publisher: American Astronomical Society
Date: 23-06-2014
Publisher: Oxford University Press (OUP)
Date: 21-08-2023
Publisher: American Astronomical Society
Date: 05-2023
Abstract: Gravitational lenses can magnify distant galaxies, allowing us to discover and characterize the stellar populations of intrinsically faint, quiescent galaxies that are otherwise extremely difficult to directly observe at high redshift from ground-based telescopes. Here, we present the spectral analysis of two lensed, quiescent galaxies at z ≳ 1 discovered by the ASTRO 3D Galaxy Evolution with Lenses survey: AGEL 1323 ( M * ∼ 10 11.1 M ⊙ , z = 1.016, μ ∼ 14.6) and AGEL 0014 ( M * ∼ 10 11.5 M ⊙ , z = 1.374, μ ∼ 4.3). We measured the age, [Fe/H], and [Mg/Fe] of the two lensed galaxies using deep, rest-frame-optical spectra (S/N ≳40 Å −1 ) obtained on the Keck I telescope. The ages of AGEL 1323 and AGEL 0014 are 5.6 − 0.8 + 0.8 Gyr and 3.1 − 0.3 + 0.8 Gyr, respectively, indicating that most of the stars in the galaxies were formed less than 2 Gyr after the Big Bang. Compared to nearby quiescent galaxies of similar masses, the lensed galaxies have lower [Fe/H] and [Mg/H]. Surprisingly, the two galaxies have comparable [Mg/Fe] to similar-mass galaxies at lower redshifts, despite their old ages. Using a simple analytic chemical evolution model connecting the instantaneously recycled element Mg with the mass-loading factors of outflows averaged over the entire star formation history, we found that the lensed galaxies may have experienced enhanced outflows during their star formation compared to lower-redshift galaxies, which may explain why they quenched early.
Publisher: American Astronomical Society
Date: 25-03-2019
Publisher: American Astronomical Society
Date: 12-2005
DOI: 10.1086/497001
Publisher: American Astronomical Society
Date: 03-03-2016
Publisher: American Astronomical Society
Date: 27-07-2010
Publisher: American Astronomical Society
Date: 18-12-2019
Publisher: American Astronomical Society
Date: 15-04-2013
Publisher: American Astronomical Society
Date: 06-2007
DOI: 10.1086/513738
Publisher: American Astronomical Society
Date: 22-02-2021
Publisher: American Astronomical Society
Date: 11-11-2011
Publisher: American Astronomical Society
Date: 21-08-2014
Publisher: American Astronomical Society
Date: 13-04-2017
Publisher: American Astronomical Society
Date: 27-01-2016
Publisher: American Astronomical Society
Date: 10-09-1997
DOI: 10.1086/310844
Publisher: American Astronomical Society
Date: 03-06-2015
Publisher: American Astronomical Society
Date: 10-04-2007
DOI: 10.1086/510061
Publisher: American Astronomical Society
Date: 18-02-2014
Publisher: American Astronomical Society
Date: 24-08-2016
Publisher: Cambridge University Press (CUP)
Date: 03-2004
Publisher: American Astronomical Society
Date: 02-04-2015
Publisher: Springer Science and Business Media LLC
Date: 25-05-2020
Publisher: American Astronomical Society
Date: 02-2023
Abstract: We present a new rest-frame color–color selection method using synthetic u s − g s and g s − i s , ( ugi ) s colors to identify star-forming and quiescent galaxies. Our method is similar to the widely used U − V versus V − J ( UVJ ) diagram. However, UVJ suffers known systematics. Spectroscopic c aigns have shown that UVJ -selected quiescent s les at z ≳ 3 include ∼10%–30% contamination from galaxies with dust-obscured star formation and strong emission lines. Moreover, at z 3, UVJ colors are extrapolated because the rest-frame band shifts beyond the coverage of the deepest bandpasses at μ m (typically Spitzer/IRAC 4.5 μ m or future JWST/NIRCam observations). We demonstrate that ( ugi ) s offers improvements to UVJ at z 3, and can be applied to galaxies in the JWST era. We apply ( ugi ) s selection to galaxies at 0.5 z 6 from the (observed) 3D-HST and UltraVISTA catalogs, and to the (simulated) JAGUAR catalogs. We show that extrapolation can affect ( V − J ) 0 color by up to 1 mag, but changes ( g s − i s ) 0 color by ≤0.2 mag, even at z ≃ 6. While ( ugi ) s -selected quiescent s les are comparable to UVJ in completeness (both achieve ∼85%–90% at z = 3–3.5), ( ugi ) s reduces contamination in quiescent s les by nearly a factor of 2, from ≃35% to ≃17% at z = 3, and from ≃60% to ≃33% at z = 6. This leads to improvements in the true-to-false-positive ratio (TP/FP), where we find TP/FP ≳2.2 for ( ugi ) s at z ≃ 3.5 − 6, compared to TP/FP 1 for UVJ -selected s les. This indicates that contaminants will outnumber true quiescent galaxies in UVJ at these redshifts, while ( ugi ) s will provide higher-fidelity s les.
Publisher: Oxford University Press (OUP)
Date: 02-05-2011
Publisher: American Astronomical Society
Date: 10-2022
Abstract: Imaging data is the principal observable required to use galaxy-scale strong lensing in a multitude of applications in extragalactic astrophysics and cosmology. In this paper, we develop Lensing Exposure Time Calculator (L ensing ETC jshajib/LensingETC ) to optimize the efficiency of telescope-time usage when planning multifilter imaging c aigns for galaxy-scale strong lenses. This tool simulates realistic data tailored to specified instrument characteristics and then automatically models them to assess the power of the data in constraining lens model parameters. We demonstrate a use case of this tool by optimizing a two-filter observing strategy (in the IR and ultraviolet-visual (UVIS)) within the limited exposure time per system allowed by a Hubble Space Telescope (HST) Snapshot program. We find that higher resolution is more advantageous to gain constraining power on the lensing observables, when there is a trade-off between signal-to-noise ratio and resolution for ex le, between the UVIS and IR filters of the HST. We also find that, whereas a point-spread function (PSF) with sub-Nyquist s ling allows the s le mean for a model parameter to be robustly recovered for both galaxy–galaxy and point-source lensing systems, a sub-Nyquist-s led PSF introduces a larger scatter than a Nyquist-s led one in the deviation from the ground truth for point-source lens systems.
Publisher: American Astronomical Society
Date: 03-02-2017
Publisher: American Astronomical Society
Date: 20-07-2017
Publisher: American Astronomical Society
Date: 10-07-2004
DOI: 10.1086/421237
Publisher: American Astronomical Society
Date: 09-06-2005
DOI: 10.1086/432090
Publisher: Oxford University Press (OUP)
Date: 22-01-2016
Publisher: American Astronomical Society
Date: 18-07-2016
Publisher: American Astronomical Society
Date: 10-06-2003
DOI: 10.1086/374831
Publisher: American Astronomical Society
Date: 20-05-2014
Publisher: American Astronomical Society
Date: 20-04-2006
DOI: 10.1086/504714
Publisher: American Astronomical Society
Date: 05-02-2020
Publisher: EDP Sciences
Date: 10-2015
Publisher: American Astronomical Society
Date: 31-10-2016
Publisher: American Astronomical Society
Date: 23-07-2015
Publisher: American Astronomical Society
Date: 12-08-2011
Publisher: American Astronomical Society
Date: 24-05-2013
Publisher: American Astronomical Society
Date: 21-07-2020
Publisher: American Astronomical Society
Date: 16-09-2015
Publisher: Oxford University Press (OUP)
Date: 21-08-2023
Publisher: American Astronomical Society
Date: 03-06-2010
Publisher: Oxford University Press (OUP)
Date: 08-03-2018
Publisher: Cambridge University Press (CUP)
Date: 08-2013
DOI: 10.1017/S1743921313004845
Abstract: Massive Brightest Cluster Galaxies (BCGs) are observed to have a range of angular momenta, suggesting a variety of merging histories.
Publisher: EDP Sciences
Date: 10-2018
DOI: 10.1051/0004-6361/201833070
Abstract: We present Keck–MOSFIRE H and K spectra for a s le of 24 candidate quiescent galaxies at 3 z 4, identified from their rest-frame U V J colors and photometric redshifts in the ZFOURGE and 3DHST surveys. With median integration times of one hour in H and five in K , we obtain spectroscopic redshifts for half of the s le, using either Balmer absorption lines or nebular emission lines. We confirm the high accuracy of the photometric redshifts for this spectroscopically-confirmed s le, with a median | Z phot − Z spec |/(1 + Z spec ) of 1.2%. Two galaxies turn out to be dusty H α emitters at lower redshifts ( z 2.5), and these are the only two detected in the sub-mm with ALMA. High equivalent-width [O III ] emission is observed in two galaxies, contributing up to 30% of the K -band flux and mimicking the U V J colors of an old stellar population. This implies a failure rate of only 20% for the U V J selection at these redshifts. Lastly, Balmer absorption features are identified in four galaxies, among the brightest of the s le, confirming the absence of OB stars. We then modeled the spectra and photometry of all quiescent galaxies with a wide range of star-formation histories. We find specific star-formation rates (sSFR) lower than 0.15 Gyr −1 (a factor of ten below the main sequence) for all but one galaxy, and lower than 0.01 Gyr −1 for half of the s le. These values are consistent with the observed Hβ and [O II ] luminosities, and the ALMA non-detections. The implied formation histories reveal that these galaxies have quenched on average 300 Myr prior to being observed, between z = 3.5 and 5, and that half of their stars were formed by z ∼ 5.5 with a mean SFR ~ 300 M ⊙ yr −1 . We finally compared the U V J selection to a selection based instead on the sSFR, as measured from the photometry. We find that galaxies a factor of ten below the main sequence are 40% more numerous than U V J -selected quiescent galaxies, implying that the U V J selection is pure but incomplete. Current models fail at reproducing our observations, and underestimate either the number density of quiescent galaxies by more than an order of magnitude, or the duration of their quiescence by a factor two. Overall, these results confirm the existence of an unexpected population of quiescent galaxies at z 3, and offer the first insights on their formation histories.
Publisher: American Astronomical Society
Date: 27-07-2016
Publisher: American Astronomical Society
Date: 14-11-2005
DOI: 10.1086/498707
Publisher: EDP Sciences
Date: 03-2018
DOI: 10.1051/0004-6361/201731917
Abstract: We obtained ALMA spectroscopy and deep imaging to investigate the origin of the unexpected sub-millimeter emission toward the most distant quiescent galaxy known to date, ZF-COSMOS-20115 at z = 3.717. We show here that this sub-millimeter emission is produced by another massive ( M * ~ 10 11 M ⊙ ), compact ( r 1∕2 = 0.67 ± 0.14 kpc) and extremely obscured galaxy ( A V ~ 3.5), located only 0.43 ′′ (3.1 kpc) away from the quiescent galaxy. We dub the quiescent and dusty galaxies Jekyll and Hyde, respectively. No dust emission is detected at the location of the quiescent galaxy, implying SFR 13 M ⊙ yr −1 which is the most stringent upper limit ever obtained for a quiescent galaxy at these redshifts. The two sources are spectroscopically confirmed to lie at the same redshift thanks to the detection of [C II ] 158 in Hyde ( z = 3.709), which provides one the few robust redshifts for a highly-obscured “ H -dropout” galaxy ( H − [4.5] = 5.1 ± 0.8). The [C II ] line shows a clear rotating-disk velocity profile which is blueshifted compared to the Balmer lines of Jekyll by 549 ± 60 km s −1 , demonstrating that it is produced by another galaxy. Careful de-blending of the Spitzer imaging confirms the existence of this new massive galaxy, and its non-detection in the Hubble images requires extremely red colors and strong attenuation by dust. Full modeling of the UV-to-far-IR emission of both galaxies shows that Jekyll has fully quenched at least 200Myr prior to observation and still presents a challenge for models, while Hyde only harbors moderate star-formation with SFR ≲ 120 M ⊙ yr −1 , and is located at least a factor 1.4 below the z ~ 4 main sequence. Hyde could also have stopped forming stars less than 200 Myr before being observed this interpretation is also suggested by its compactness comparable to that of z ~ 4 quiescent galaxies and its low [C II ]/FIR ratio, but significant on-going star-formation cannot be ruled out. Lastly, we find that despite its moderate SFR, Hyde hosts a dense reservoir of gas comparable to that of the most extreme starbursts. This suggests that whatever mechanism has stopped or reduced its star-formation must have done so without expelling the gas outside of the galaxy. Because of their surprisingly similar mass, compactness, environment and star-formation history, we argue that Jekyll and Hyde can be seen as two stages of the same quenching process, and provide a unique laboratory to study this poorly understood phenomenon.
Publisher: American Astronomical Society
Date: 31-03-2020
Publisher: American Astronomical Society
Date: 20-07-2012
Publisher: Oxford University Press (OUP)
Date: 18-04-2018
DOI: 10.1093/MNRAS/STY961
Publisher: American Astronomical Society
Date: 09-2021
Publisher: American Astronomical Society
Date: 17-10-2014
Publisher: American Astronomical Society
Date: 03-07-2007
DOI: 10.1086/520577
Publisher: Oxford University Press (OUP)
Date: 22-06-2017
Publisher: American Astronomical Society
Date: 14-10-2008
DOI: 10.1086/593978
Publisher: American Astronomical Society
Date: 20-02-2014
Publisher: American Astronomical Society
Date: 15-10-2009
Publisher: American Astronomical Society
Date: 28-06-2016
Publisher: American Astronomical Society
Date: 22-06-2016
Publisher: American Astronomical Society
Date: 28-09-2011
Publisher: American Astronomical Society
Date: 15-06-2017
Publisher: American Astronomical Society
Date: 11-02-2016
Location: United States of America
Location: United States of America
Start Date: 07-2017
End Date: 12-2024
Amount: $30,300,000.00
Funder: Australian Research Council
View Funded Activity