arXiv subjects

Michael Florian

Publications and source records attributed to Michael Florian.

30 records · Page 2Linked to original sources

arXiv2022

JWST/NIRCam Coronagraphy: Commissioning and First On-Sky Results

In a cold and stable space environment, the James Webb Space Telescope (JWST or "Webb") reaches unprecedented sensitivities at wavelengths beyond 2 microns, serving most fields of astrophysics. It also extends the parameter space of high-contrast imaging in the near and mid-infrared. Launched in late 2021, JWST underwent a six month commissioning period. In this contribution we focus on the NIRCam Coronagraphy mode which was declared "science ready" on July 10 2022, the last of the 17 JWST observing modes. Essentially, this mode will allow to detect fainter/redder/colder (less massive for a given age) self-luminous exoplanets as well as other faint astrophysical signal in the vicinity of any bright object (stars or galaxies). Here we describe some of the steps and hurdles the commissioning team went through to achieve excellent performances. Specifically, we focus on the Coronagraphic Suppression Verification activity. We were able to produce firm detections at 3.35$μ$m of the white dwarf companion HD 114174 B which is at a separation of $\simeq$ 0.5" and a contrast of $\simeq$ 10 magnitudes ($10^{4}$ fainter than the K$\sim$5.3 mag host star). We compare these first on-sky images with our latest, most informed and realistic end-to-end simulations through the same pipeline. Additionally we provide information on how we succeeded with the target acquisition with all five NIRCam focal plane masks and their four corresponding wedged Lyot stops.

astro-ph.IM↗

arXiv2022

RELICS: Small-scale Star Formation in Lensed Galaxies at $z = 6-10$

Detailed observations of star forming galaxies at high redshift are critical to understand the formation and evolution of the earliest galaxies. Gravitational lensing provides an important boost, allowing observations at physical scales unreachable in unlensed galaxies. We present three lensed galaxies from the RELICS survey at $z_{phot} = 6 - 10$, including the most highly magnified galaxy at $z_{phot} \sim 6$ (WHL0137-zD1, dubbed the Sunrise Arc), the brightest known lensed galaxy at $z_{phot} \sim 6$ (MACS0308-zD1), and the only spatially resolved galaxy currently known at $z_{phot} \sim 10$ (SPT0615-JD). The Sunrise Arc contains seven star-forming clumps with delensed radii as small as 3 pc, the smallest spatial scales yet observed in a $z>6$ galaxy, while SPT0615-JD contains features measuring a few tens of parsecs. MACS0308-zD1 contains a $r\sim 30$ pc clump with a star formation rate (SFR) of $\sim 3 M_{\odot} \textrm{ yr}^{-1}$, giving it a SFR surface density of $Σ_{SFR} \sim 10^3 M_{\odot}\textrm{ yr}^{-1}\textrm{ kpc}^{-2}$. These galaxies provide a unique window into small scale star formation during the Epoch of Reionization. They will be excellent targets for future observations with JWST, including one approved program targeting the Sunrise Arc.

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arXiv2020

A Comparison of Rest-frame Ultraviolet and Optical Emission-Line Diagnostics in the Lensed Galaxy SDSS J1723+3411 at Redshift z=1.3293

For the extremely bright lensed galaxy SDSS J1723+3411 at z=1.3293 , we analyze spatially integrated MMT, Keck, and Hubble Space Telescope spectra that fully cover the rest-frame wavelength range of 1400 to 7200 Angstroms. We also analyze near-IR spectra from Gemini that cover H alpha for a portion of the lensed arc. We report fluxes for 42 detected emission lines, and upper limits for an additional 22. This galaxy has extreme emission line ratios and high equivalent widths that are characteristic of extreme emission-line galaxies. We compute strong emission line diagnostics from both the rest-frame optical and rest-frame ultraviolet (UV), to constrain physical conditions and test the spectral diagnostics themselves. We tightly determine the nebular physical conditions using the most reliable diagnostics, and then compare to results from other diagnostics. We find disappointing performance from the UV--only diagnostics: they either are unable to measure the metallicity or dramatically under-estimate it; they over-estimate the pressure; and the UV diagnostic of ionization parameter has a strong metallicity dependence in this regime. Based on these results, we suggest that upcoming James Webb Space Telescope spectroscopic surveys of galaxies in the reionization epoch should invest the additional integration time to capture the optical [O II] and [O III] emission lines, and not rely solely on the rest-frame UV emission lines. We make available the spectra; they represent one of the highest-quality emission line spectral atlases of star-forming galaxy available beyond the local universe, and will aid planning observations with JWST.

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arXiv2019

Rest-frame UV and optical emission line diagnostics of ionised gas properties: a test case in a star-forming knot of a lensed galaxy at z~1.7

We examine the diagnostic power of rest-frame ultraviolet (UV) nebular emission lines, and compare them to more commonly used rest-frame optical emission lines, using the test case of a single star-forming knot of the bright lensed galaxy RCSGA 032727-132609 at redshift z~1.7. This galaxy has complete coverage of all the major rest-frame UV and optical emission lines from Magellan/MagE and Keck/NIRSPEC. Using the full suite of diagnostic lines, we infer the physical properties: nebular electron temperature (T_e), electron density (n_e), oxygen abundance (log(O/H)), ionisation parameter (log(q)) and interstellar medium (ISM) pressure (log(P/k)). We examine the effectiveness of the different UV, optical and joint UV-optical spectra in constraining the physical conditions. Using UV lines alone we can reliably estimate log(q), but the same is difficult for log(O/H). UV lines yield a higher (~1.5 dex) log(P/k) than the optical lines, as the former probes a further inner nebular region than the latter. For this comparison, we extend the existing Bayesian inference code IZI, adding to it the capability to infer ISM pressure simultaneously with metallicity and ionisation parameter. This work anticipates future rest-frame UV spectral datasets from the James Webb Space Telescope (JWST) at high redshift and from the Extremely Large Telescope (ELT) at moderate redshift.

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arXiv2019

Astro2020 APC White Paper: The Early Career Perspective on the Coming Decade, Astrophysics Career Paths, and the Decadal Survey Process

In response to the need for the Astro2020 Decadal Survey to explicitly engage early career astronomers, the National Academies of Sciences, Engineering, and Medicine hosted the Early Career Astronomer and Astrophysicist Focus Session (ECFS) on October 8-9, 2018 under the auspices of Committee of Astronomy and Astrophysics. The meeting was attended by fifty six pre-tenure faculty, research scientists, postdoctoral scholars, and senior graduate students, as well as eight former decadal survey committee members, who acted as facilitators. The event was designed to educate early career astronomers about the decadal survey process, to solicit their feedback on the role that early career astronomers should play in Astro2020, and to provide a forum for the discussion of a wide range of topics regarding the astrophysics career path. This white paper presents highlights and themes that emerged during two days of discussion. In Section 1, we discuss concerns that emerged regarding the coming decade and the astrophysics career path, as well as specific recommendations from participants regarding how to address them. We have organized these concerns and suggestions into five broad themes. These include (sequentially): (1) adequately training astronomers in the statistical and computational techniques necessary in an era of "big data", (2) responses to the growth of collaborations and telescopes, (3) concerns about the adequacy of graduate and postdoctoral training, (4) the need for improvements in equity and inclusion in astronomy, and (5) smoothing and facilitating transitions between early career stages. Section 2 is focused on ideas regarding the decadal survey itself, including: incorporating early career voices, ensuring diverse input from a variety of stakeholders, and successfully and broadly disseminating the results of the survey.

astro-ph.IM↗

arXiv2019

The production and escape of ionizing photons from galaxies over cosmic time (Astro2020 Science White Paper)

The ionizing photons produced by massive stars are key actors in galaxy evolution. Ionizing photon production and escape is poorly understood. Improved space-based, spatially-resolved, multiplexed spectroscopic capabilities covering observed wavelengths of 1000 to 3000 Angstrom, in concert with spectroscopy from the ELTs and JWST, would lead to definitive answers as to how ionizing photons are produced and leaked, what populations of galaxies are responsible for ionizing photon leakage, what determines whether escape is possible, and how ionizing galaxy populations evolve over cosmic time.

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arXiv2017

Spatially Resolved Patchy Lyman-$α$ Emission Within the Central Kiloparsec of a Strongly Lensed Quasar Host Galaxy at z = 2.8

We report the detection of extended Lyman-$α$ emission from the host galaxy of SDSS~J2222+2745, a strongly lensed quasar at $z = 2.8$. Spectroscopic follow-up clearly reveals extended Lyman-$α$ in emission between two images of the central active galactic nucleus (AGN). We reconstruct the lensed quasar host galaxy in the source plane by applying a strong lens model to HST imaging, and resolve spatial scales as small as $\sim$200 parsecs. In the source plane we recover the host galaxy morphology to within a few hundred parsecs of the central AGN, and map the extended Lyman-$α$ emission to its physical origin on one side of the host galaxy at radii $\sim$0.5-2 kpc from the central AGN. There are clear morphological differences between the Lyman-$α$ and rest-frame ultraviolet stellar continuum emission from the quasar host galaxy. Furthermore, the relative velocity profiles of quasar Lyman-$α$, host galaxy Lyman-$α$, and metal lines in outflowing gas reveal differences in the absorbing material affecting the AGN and host galaxy. These data indicate the presence of patchy local intervening gas in front of the central quasar and its host galaxy. This interpretation is consistent with the central luminous quasar being obscured across a substantial fraction of its surrounding solid angle, resulting in strong anisotropy in the exposure of the host galaxy to ionizing radiation from the AGN. This work demonstrates the power of strong lensing-assisted studies to probe spatial scales that are currently inaccessible by other means.

astro-ph.GA↗

arXiv2017

Star Formation at z=2.481 in the Lensed Galaxy SDSS J1110+6459, I: Lens Modeling and Source Reconstruction

Using the combined resolving power of the Hubble Space Telescope and gravitational lensing, we resolve star-forming structures in a z~2.5 galaxy on scales much smaller than the usual kiloparsec diffraction limit of HST. SGAS J111020.0+645950.8 is a clumpy, star forming galaxy lensed by the galaxy cluster SDSS J1110+6459 at z = 0.659, with a total magnification ~30x across the entire arc. We use a hybrid parametric/non-parametric strong lensing mass model to compute the deflection and magnification of this giant arc, reconstruct the light distribution of the lensed galaxy in the source plane, and resolve the star formation into two dozen clumps. We develop a forward-modeling technique to model each clump in the source plane. We ray trace the model to the image plane, convolve with the instrumental point spread function (PSF), and compare with the GALFIT model of the clumps in the image plane, which decomposes clump structure from more extended emission. This technique has the advantage, over ray tracing, by accounting for the asymmetric lensing shear of the galaxy in the image plane and the instrument PSF. At this resolution, we can begin to study star formation on a clump-by-clump basis, toward the goal of understanding feedback mechanisms and the buildup of exponential disks at high redshift.

astro-ph.GA↗

arXiv2017

Star Formation at z=2.481 in the Lensed Galaxy SDSS J1110+6459: Star Formation down to 30 parsec scales

We present measurements of the surface density of star formation, the star-forming clump luminosity function, and the clump size distribution function, for the lensed galaxy SGAS J111020.0+645950.8 at a redshift of z=2.481. The physical size scales that we probe, radii r=30--50 pc, are considerably smaller scales than have yet been studied at these redshifts. The star formation surface density we find within these small clumps is consistent with surface densities measured previously for other lensed galaxies at similar redshift. Twenty-two percent of the rest-frame ultraviolet light in this lensed galaxy arises from small clumps, with r<100 pc. Within the range of overlap, the clump luminosity function measured for this lensed galaxy is remarkably similar to those of z~0 galaxies. In this galaxy, star-forming regions smaller than 100 pc---physical scales not usually resolved at these redshifts by current telescopes---are important locations of star formation in the distant universe. If this galaxy is representative, this may contradict the theoretical picture in which the critical size scale for star formation in the distant universe is of order 1 kiloparsec. Instead, our results suggest that current telescopes have not yet resolved the critical size scales of star-forming activity in galaxies over most of cosmic time.

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arXiv2016

Magellan LDSS3 emission confirmation of galaxies hosting metal-rich Lyman-alpha absorption systems

Using the Low Dispersion Survey Spectrograph 3 at the Magellan II Clay Telescope, we target {candidate absorption host galaxies} detected in deep optical imaging {(reaching limiting apparent magnitudes of 23.0-26.5 in $g, r, i,$ and $z$ filters) in the fields of three QSOs, each of which shows the presence of high metallicity, high $N_{\rm HI}$ absorption systems in their spectra (Q0826-2230: $z_{abs}$=0.9110, Q1323-0021: $z_{abs}=0.7160$, Q1436-0051: $z_{abs}=0.7377, 0.9281$). We confirm three host galaxies {at redshifts 0.7387, 0.7401, and 0.9286} for two of the Lyman-$α$ absorption systems (one with two galaxies interacting). For these systems, we are able to determine the star formation rates (SFRs); impact parameters (from previous imaging detections); the velocity shift between the absorption and emission redshifts; and, for one system, also the emission metallicity.} Based on previous photometry, we find these galaxies have L$>$L$^{\ast}$. The [O II] SFRs for these galaxies are in the range $11-25$ M$_{\odot}$ yr$^{-1}$ {(uncorrected for dust)}, while the impact parameters lie in the range $35-54$ kpc. {Despite the fact that we have confirmed galaxies at 50 kpc from the QSO, no gradient in metallicity is indicated between the absorption metallicity along the QSO line of sight and the emission line metallicity in the galaxies.} We confirm the anti-correlation between impact parameter and $N_{\rm HI}$ from the literature. We also report the emission redshift of five other galaxies: three at $z_{em}>z_{QSO}$, and two (L$<$L$^{\ast}$) at $z_{em}<z_{QSO}$ not corresponding to any known absorption systems.

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arXiv2014

A Thirty Kiloparsec Chain of "Beads on a String" Star Formation Between Two Merging Early Type Galaxies in the Core of a Strong-Lensing Galaxy Cluster

New Hubble Space Telescope ultraviolet and optical imaging of the strong-lensing galaxy cluster SDSS J1531+3414 (z=0.335) reveals two centrally dominant elliptical galaxies participating in an ongoing major merger. The interaction is at least somewhat rich in cool gas, as the merger is associated with a complex network of nineteen massive superclusters of young stars (or small tidal dwarf galaxies) separated by ~1 kpc in projection from one another, combining to an estimated total star formation rate of ~5 solar masses per year. The resolved young stellar superclusters are threaded by narrow H-alpha, [O II], and blue excess filaments arranged in a network spanning ~27 kpc across the two merging galaxies. This morphology is strongly reminiscent of the well-known "beads on a string" mode of star formation observed on kpc-scales in the arms of spiral galaxies, resonance rings, and in tidal tails between interacting galaxies. Nevertheless, the arrangement of this star formation relative to the nuclei of the two galaxies is difficult to interpret in a dynamical sense, as no known "beads on a string" systems associated with kpc-scale tidal interactions exhibit such lopsided morphology relative to the merger participants. In this Letter we present the images and follow-up spectroscopy, and discuss possible physical interpretations for the unique arrangement of the young stellar clusters. While we suggest that this morphology is likely to be dynamically short-lived, a more quantitative understanding awaits necessary multiwavelength follow-up, including optical integral field spectroscopy, ALMA sub-mm interferometry, and Chandra X-ray imaging.

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arXiv2014

The Physical Conditions, Metallicity and Metal Abundance Ratios In a Highly Magnified Galaxy at z = 3.6252

We present optical and near-IR imaging and spectroscopy of SGAS J105039.6$+$001730, a strongly lensed galaxy at z $=$ 3.6252 magnified by $>$30$\times$, and derive its physical properties. We measure a stellar mass of log(M$_{*}$/M$_{\odot}$) $=$ 9.5 $\pm$ 0.35, star formation rates from [O II]$λ$$λ$3727 and H-$β$ of 55 $\pm$ 20 and 84 $\pm$ 17 M$_{\odot}$ yr$^{-1}$, respectively, an electron density of n$_{e} \leq$ 10$^{3}$ cm$^{-2}$, an electron temperature of T$_{e} \leq$ 14000 K, and a metallicity of 12+log(O/H) $=$ 8.3 $\pm$ 0.1. The strong C III]$λ$$λ$1907,1909 emission and abundance ratios of C, N, O and Si are consistent with well-studied starbursts at z $\sim$ 0 with similar metallicities. Strong P Cygni lines and He II$λ$1640 emission indicate a significant population of Wolf-Rayet stars, but synthetic spectra of individual populations of young, hot stars do not reproduce the observed integrated P Cygni absorption features. The rest-frame UV spectral features are indicative of a young starburst with high ionization, implying either 1) an ionization parameter significantly higher than suggest by rest-frame optical nebular lines, or 2) differences in one or both of the initial mass function and the properties of ionizing spectra of massive stars. We argue that the observed features are likely the result of a superposition of star forming regions with different physical properties. These results demonstrate the complexity of star formation on scales smaller than individual galaxies, and highlight the importance of systematic effects that result from smearing together the signatures of individual star forming regions within galaxies.

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