Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Yu-Heng Lin
Claudia Scarlata
Matthew Hayes
Anna Feltre
Stephane Charlot
Angela Bongiorno
Petri Väisänen
Moses Mogotsi
Abstract： We present S82-20, an unusual redshift $\approx$3 object identified in SDSS-Stripe 82 broad-band images. The rest-frame ultraviolet spectrum of S82-20 shows emission lines from highly ionized species, including HeII $\lambda$1640, and the CIV $\lambda\lambda$1548, 1550 and OVI $\lambda\lambda$1032, 1038 doublets. The high Ly$\alpha$ luminosity ($3.5\times 10^{44}$ erg s$^{-1}$), the high emission line equivalent widths ($>200$\r{A} for Ly$\alpha$), the FWHM of the emission lines ($<800$km s$^{-1}$), and the high ionization OVI line strongly support the interpretation that S82-20 is a Type~II QSO. However, photoionization models using Type~II QSO do not fully explain the measured CIV/HeII line ratio, which requires either some contribution from star-formation or high velocity shocks. Additionally, S82-20 is not detected at wavelengths longer than 2$\mu$m, in tension with the expectation of isotropically IR emission of a luminous QSO. We consider the possibility that S82-20 is a rare example of a changing-look QSO, observed in a temporarily low state, where the broad line region has faded, while the narrow line region still emits emission line. Otherwise, it may be a rare case of the short phase of the life of a massive galaxy, in which active star formation and accretion onto a supermassive black hole coexist.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Matilde Mingozzi
Bethan L. James
Karla Z. Arellano-Córdova
Danielle A. Berg
Peter Senchyna
John Chisholm
Jarle Brinchmann
Alessandra Aloisi
Ricardo Amorín
Stephane Charlot
Anna Feltre
Matthew J. Hayes
Tim Heckman
Alaina Henry
Svea Hernandez
Nimisha Kumari
Claus Leitherer
Mario Llerena
Crystal L. Martin
Themiya Nanayakkara
Abstract： The COS Legacy Archive Spectroscopic SurveY (CLASSY) HST/COS treasury program provides the first high-resolution spectral catalogue of 45 local high-z analogues in the UV (1200-2000{\AA}) to investigate their stellar and gas properties. We present a toolkit of UV interstellar medium (ISM) diagnostics, analyzing the main emission lines of CLASSY spectra (i.e., NIV]{\lambda}{\lambda}1483,87, CIV{\lambda}{\lambda}1548,51, HeII{\lambda}1640, OIII]{\lambda}{\lambda}1661,6, SiIII]{\lambda}{\lambda}1883,92, CIII]{\lambda}{\lambda}1907,9). Specifically, we focus our investigation on providing accurate diagnostics for reddening, electron density and temperature, gas-phase metallicity and ionization parameter, taking into account the different ionization zones of the ISM. We calibrate our UV toolkit using well-known optical diagnostics, analyzing archival optical spectra for all the CLASSY targets. We find that UV density diagnostics estimate ne values that are ~1-2 dex higher (e.g., ne(CIII]{\lambda}{\lambda}1907,9)~10^4cm^{-3}) than those inferred from their optical counterparts (e.g., ne([SII]{\lambda}{\lambda}6717,31)~10^2cm^{-3}). Te derived from the hybrid ratio OIII]{\lambda}1666/[OIII]{\lambda}5007 proves to be a reliable Te diagnostic, with differences in 12+log(O/H) within ~+/-0.3dex. We also investigate the relation between the stellar and gas E(B-V), finding consistent values at high specific star formation rates, while at low sSFR we confirm an excess of dust attenuation in the gas. Finally, we investigate UV line ratios and equivalent widths to provide correlations with 12+log(O/H) and log(U), but note there are degeneracies between the two. With this suite of UV-based diagnostics, we illustrate the pivotal role CLASSY plays in understanding the chemical and physical properties of high-z systems that JWST can observe in the rest-frame UV.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Mengtao Tang
Daniel P. Stark
Richard S. Ellis
Stéphane Charlot
Anna Feltre
Alice E. Shapley
Ryan Endsley
Abstract： Reionisation-era galaxies often display intense nebular emission lines, both in rest-frame optical ([OIII]+H$\beta$) and ultraviolet (UV; CIII], CIV). How such strong nebular emission is powered remains unclear, with both active galactic nuclei (AGN) and hot stars considered equally viable. The UV continuum slopes of these early systems tend to be very blue ($\beta<-2$), reflecting minimal dust obscuration, young ages, and low metallicities. This contrasts with narrow-lined AGN at $z\sim2-3$, whose UV slopes are significantly redder ($\beta>-1$) than typical star-forming systems in the reionisation era. To investigate the properties of AGN in the reionisation era, we have conducted a search for potential examples of rare analogues with blue continua at intermediate redshift ($z\sim2-3$). Our goals are to determine whether AGN with intense line emission and blue continua exist and thereby to establish the range of rest-frame UV and optical line ratios in this population. In this paper we report the detection of a X-ray luminous AGN at $z=3.21$ (UDS-24561) with extreme [OIII]+H$\beta$ line emission (EW $=1300$ \r{A}) and a blue UV continuum slope ($\beta=-2.34$). MMT/Binospec and Keck/MOSFIRE spectra indicate rest-frame UV line ratios consistent with AGN photoionisation models and rest-frame optical lines with both a narrow component (FWHM $=154$ km$/$s) and extended broad wings (FWHM $=977$ km$/$s), consistent with outflowing gas. We describe how such objects can be identified in future JWST emission line surveys in the reionisation era, thereby providing a valuable census of AGN activity at $z>6$ and understanding their contribution to cosmic reionisation.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Lukas J. Furtak
Adi Zitrin
Adèle Plat
Seiji Fujimoto
Bingjie Wang
Erica J. Nelson
Ivo Labbé
Rachel Bezanson
Gabriel B. Brammer
Pieter van Dokkum
Ryan Endsley
Karl Glazebrook
Jenny E. Greene
Joel Leja
Sedona H. Price
Renske Smit
Daniel P. Stark
John R. Weaver
Katherine E. Whitaker
Hakim Atek
Abstract： Recent JWST/NIRcam imaging taken for the ultra-deep UNCOVER program reveal a very red, triply imaged, compact dropout object at $z_{\mathrm{phot}}\simeq7.66$ which is prominently lensed by the galaxy cluster Abell 2744 ($z_{\mathrm{d}}=0.308$). All three images are very compact, i.e. unresolved, with an inferred de-lensed size upper limit of $r_{e}\lesssim35$ pc. The observed F444W magnitude of the three images is $m\sim25-26$ AB and the source's absolute UV magnitude is $M_{\mathrm{UV},1450}=-16.81\pm0.09$, after correcting for magnification. From the sum of observed fluxes and from a spectral energy distribution (SED) fit we obtain lower limits on the bolometric luminosities of $L_{\mathrm{bol}}\gtrsim10^{43} \frac{\mathrm{erg}}{\mathrm{s}}$ and $L_{\mathrm{bol}}\gtrsim10^{44} \frac{\mathrm{erg}}{\mathrm{s}}$ for the source, respectively. Based on its compact, point-like appearance, its positions in color-color and $M_{\mathrm{UV}}$-size diagrams and the SED analysis, we tentatively conclude that this object could be a faint quasar-like object, i.e., an extreme emission line object whose nebular emission is boosted by an active galactic nucleus (AGN). We discuss various alternative origins for the object's emission features, including a massive star cluster, a cluster of Population III, supermassive, or dark stars, or a direct-collapse black hole. Although populations of red galaxies at similar photometric redshifts have been detected with JWST, this object is unique in that its high-redshift nature is corroborated geometrically by lensing, that it is unresolved despite being magnified -- and thus intrinsically even more compact -- and that it occupies notably distinct regions in both size-luminosity and color-color space. The planned UNCOVER JWST/NIRSpec observations (scheduled in Cycle 1) will enable a more detailed analysis of this object.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Roland Bacon
Jarle Brinchmann
Simon Conseil
Michael Maseda
Themiya Nanayakkara
Martin Wendt
Raphael Bacher
David Mary
Peter M. Weilbacher
Davor Krajnovic
Leindert Boogaard
Nicolas Bouche
Thierry Contini
Benoit Epinat
Anna Feltre
Yucheng Guo
Christian Herenz
Wolfram Kollatschny
Haruka Kusakabe
Floriane Leclercq
Abstract： We present the second data release of the MUSE Hubble UDF surveys, which includes the deepest spectroscopic survey ever performed. The MUSE data, with their 3D content, amazing depth, wide spectral range, and excellent spatial and medium spectral resolution, are rich in information. This update of the first release incorporates a new 141-hour adaptive-optics-assisted MXDF field (1' diameter FoV) in addition to the reprocessed 10-hour mosaic (3'x3') and the single 31-hour deep field (1'x1'). We have securely identified and measured the redshift of 2221 sources, an increase of 41% compared to the first release. With the exception of 8 stars, the collected sample consists of 25 nearby galaxies (z < 0.25), 677 OII emitters (z=0.25-1.5), 201 galaxies in the MUSE redshift desert range (z=1.5-2.8), and 1308 LAEs (z=2.8-6.7). This represents an order of magnitude more redshifts than the collection of all spectroscopic redshifts obtained before MUSE in the Hubble UDF area (2221 vs 292). At z > 3, the difference is even more striking, with a factor of 65 increase (1308 vs 20). We compared the measured redshifts against three published photometric redshift catalogs and find the photo-z accuracy to be lower than the constraints provided by photo-z fitting codes. 80% of the galaxies have an HST counterpart. They are on average faint, with a median magnitude of 25.7 and 28.7 for the OII and Ly-alpha emitters, respectively. SED fits show that these galaxies tend to be low-mass star-forming galaxies, with a median stellar mass of 6.2 10**8 M and a median SFR of 0.4 M/yr. 20% of our catalog, or 424 galaxies, have no HST counterpart. The vast majority of these new sources are high EQW z>2.8 LAEs that are detected by MUSE thanks to their bright and asymmetric broad Ly-alpha line. We release advanced data products, specific software, and a web interface to select and download data sets.
Peer Review Status:Awaiting Review
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