arXiv subjects

Pablo G. Pérez-González

Publications and source records attributed to Pablo G. Pérez-González.

At least 109 records · Page 6Linked to original sources

arXiv2024

What is the nature of Little Red Dots and what is not, MIRI SMILES edition

We study little red dots (LRD) detected by JADES and covered by the SMILES MIRI survey. Our sample contains 31 sources, $\sim70$% detected in the two bluest MIRI bands, 40% in redder filters. The median/quartiles redshifts are $z=6.9_{5.9}^{7.7}$ (55% spectroscopic). We analyze the rest-frame ultraviolet through near/mid-infrared spectral energy distributions of LRDs combining NIRCam and MIRI observations, using a variety of modeling techniques that include emission from stars, dust, and (un)obscured active galactic nuclei (AGN). The NIRCam$-$MIRI colors, for $\geq10$ $μ$m, are bluer than direct pure emission from AGN tori; the spectral slope flattens in the rest-frame near-infrared, consistent with a 1.6 $μ$m stellar bump. Both observations imply that stellar emission makes the dominant contribution at these wavelengths, expediting a stellar mass estimation: the median/quartiles are $\log \mathrm{M_\star/M_\odot}=9.4_{9.1}^{9.7}$. The number density of LRDs is $10^{-4.0\pm0.1}$ Mpc$^{-3}$, accounting for $14\pm3$% of the global population of galaxies with similar redshifts and masses. The flat ultraviolet spectral range is dominated by young stars. The rest-frame near/mid-infrared (2-4 $μ$m) spectral slope reveals significant amounts of dust (bolometric stellar attenuation $\sim3-4$ mag) heated by strong radiation fields arising from highly embedded compact sources. Our models imply $<0.4$ kpc heating knots, containing dust-enshrouded OB stars or an AGN producing a similar radiation field, obscured by $\mathrm{A(V)}>10$ mag. We conclude that LRDs are extremely intense and compact starburst galaxies with mass-weighted ages 5-10 Myr, very efficient in producing dust, their global energy output dominated by the direct and dust-recycled emission from OB stars, with some contribution from obscured AGN in the mid-infrared.

astro-ph.GA↗

arXiv2024

Measuring the gas reservoirs in $10^{8}<$ M$_\star<10^{11}$ M$_\odot$ galaxies at $1\leq z\leq3$

Understanding the gas content in galaxies, its consumption and replenishment, remains pivotal in our comprehension of the evolution of the Universe. Numerous studies have addressed this, utilizing various observational tools and analytical methods. These include examining low-transition $^{12}$CO millimeter rotational lines and exploring the far-infrared and the (sub-)millimeter emission of galaxies. With the capabilities of present-day facilities, much of this research has been centered on relatively bright galaxies. We aim at exploring the gas reservoirs of a more general type of galaxy population at $1.0\leq z\leq 3.0$. We stack ALMA 1.1 mm data to measure the gas content of a mass-complete sample down to $\sim10^{8.6}$ M$_\odot$ at $z=1$ ($\sim10^{9.2}$ M$_\odot$ at $z=3$), extracted from the HST/CANDELS sample in GOODS-S. The sample is composed of 5,530 on average blue ($ \sim0.12$ mag, $ \sim0.81$ mag), star-forming main sequence objects ($Δ$MS$\sim-0.03$). We report measurements at $10^{10-11}$ M$_\odot$ and upper limits for the gas fractions at $10^{8-10}$ M$_\odot$. At $10^{10-11}$ M$_\odot$, our f$_{\mathrm{gas}}$, ranging from 0.32 to 0.48, agree well with other studies based on mass-complete samples down to $10^{10}$ M$_\odot$, and are lower than expected according to other works more biased to individual detections. At $10^{9-10}$ M$_\odot$, we obtain 3$σ$ upper limits for f$_{\mathrm{gas}}$ ranging from 0.69 to 0.77. These upper limits are on the level of the extrapolations of scaling relations based on mass-complete samples down to $10^{10}$ M$_\odot$. As such, it suggests that the gas content of low-mass galaxies is at most what is extrapolated from literature scaling relations. The comparison of our results with previous works reflects how the inclusion of bluer, less obscured, and more MS-like objects progressively pushes the gas level to lower values.

astro-ph.GA↗

arXiv2024

NGDEEP Epoch 1: Spatially Resolved H$α$ Observations of Disk and Bulge Growth in Star-Forming Galaxies at $z \sim$ 0.6-2.2 from JWST NIRISS Slitless Spectroscopy

We study the H$α$ equivalent width, EW(H$α$), maps of 19 galaxies at $0.6 < z < 2.2$ in the Hubble Ultra Deep Field (HUDF) derived from NIRISS slitless spectroscopy as part of the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) Survey. Our galaxies mostly lie on the star-formation main sequence with a stellar mass range of $\mathrm{10^9 - 10^{11} M_\odot}$, characterized as "typical" star-forming galaxies at these redshifts. Leveraging deep HST and JWST broad-band images, spanning 0.4-4.8 $μ$m, we perform spatially-resolved fitting of the spectral energy distributions (SEDs) for these galaxies and construct specific star formation rate (sSFR) and stellar-mass-weighted age maps with a spatial resolution of $\sim$1 kpc. The pixel-to-pixel EW(H$α$) increases with increasing sSFR and with decreasing age. The average trends are slightly different from the relations derived from integrated fluxes of galaxies from the literature, suggesting complex evolutionary trends within galaxies. We quantify the radial profiles of EW(H$α$), sSFR, and age. The majority (84%) of galaxies show positive EW(H$α$) gradients in line with the inside-out quenching scenario. A few galaxies (16%) show inverse (and flat) trends possibly due to merging or starbursts. We compare the distributions of EW(H$α$) and sSFR to the star formation history models (SFHs) as a function of galactocentric radius. We argue that the central regions of galaxies have experienced, at least one, rapid star-formation episodes, which leads to the formation of the bulge, while their outer regions (e.g., disks) grow via more smoothly varying SFHs. These results demonstrate the ability to study resolved star formation in distant galaxies with JWST NIRISS.

astro-ph.GA↗

arXiv2024

Deeper than DEEP: A Spectroscopic Survey of $z>3$ Lyman-$α$ Emitters in the Extended Groth Strip

We present a spectroscopic survey of Ly$α$ emitters in the Extended Groth Strip (EGS) field, targeting the regime near the Epoch of Reionization. Using Keck/DEIMOS, we observed 947 high-$z$ candidates with photometric redshifts from 3 $< z_\text{phot} <$ 7 and down to an $H$-band (HST/WFC3 F160W) magnitude limit of < 27.5. Observations were taken over the course of 8 nights, with integration times ranging from 4 to 7.8 hours. Our survey secured 137 unique redshifts, 126 of which are Ly$α$ emitters at 2.8 $< z <$ 6.5 with a mean redshift of $\overline{z} = 4.3$. We provide a comprehensive redshift catalog for our targets, as well as the reduced one- and two- dimensional spectra for each object. These observations will provide an important auxiliary dataset for the JWST Directors Discretionary Early Release Science (DD-ERS) program the Cosmic Evolution Early Release Science Survey (CEERS), which recently completed near- and mid-IR imaging and spectroscopy of galaxies in the EGS field.

astro-ph.GA↗

arXiv2024

MIDIS: JWST NIRCam and MIRI unveil the stellar population properties of Ly$α$-emitters and Lyman-Break galaxies at z ~ 3-7

We study the stellar population properties of 182 spectroscopically-confirmed (MUSE/VLT) Lyman-$α$ emitters (LAEs) and 450 photometrically-selected Lyman-Break galaxies (LBGs) at z = 2.8 - 6.7 in the Hubble eXtreme Deep Field (XDF). Leveraging the combined power of HST and JWST NIRCam and MIRI observations, we analyse their rest-frame UV-through-near-IR spectral energy distributions (SEDs) with MIRI playing a crucial role in robustly assessing the LAE's stellar mass and ages. Our LAEs are low-mass objects (log$_{10}$(M$_\star$[M$_\odot$]) ~ 7.5), with little or no dust extinction (E(B - V) ~ 0.1) and a blue UV continuum slope ($β$ ~ -2.2). While 75% of our LAEs are young (< 100 Myr), the remaining 25% have significantly older stellar populations (> 100 Myr). These old LAEs are statistically more massive, less extinct and have lower specific star formation rate (sSFR) compared to young LAEs. Besides, they populate the M$_\star$ - SFR plane along the main-sequence (MS) of star-forming galaxies, while young LAEs populate the starburst region. The comparison between the LAEs properties to those of a stellar-mass matched sample of LBGs shows no statistical difference between these objects, except for the LBGs redder UV continuum slope and marginally larger E(B - V) values. Interestingly, 48% of the LBGs have ages < 10 Myr and are classified as starbursts, but lack detectable Ly$α$ emission. This is likely due to HI resonant scattering and/or selective dust extinction. Overall, we find that JWST observations are crucial in determining the properties of LAEs and shedding light on the properties and similarities between LAEs and LBGs.

astro-ph.GA↗

arXiv2024

Characterizing the Average Interstellar Medium Conditions of Galaxies at $z\sim$ 5.6-9 with UV and Optical Nebular Lines

Ultraviolet (UV; rest-frame $\sim1200-2000$ A) spectra provide a wealth of diagnostics to characterize fundamental galaxy properties, such as their chemical enrichment, the nature of their stellar populations, and their amount of Lyman-continuum (LyC) radiation. In this work, we leverage publicly released JWST data to construct the rest-frame UV-to-optical composite spectrum of a sample of 63 galaxies at $5.6<z<9$, spanning the wavelength range from 1500 to 5200 A. Based on the composite spectrum, we derive an average dust attenuation $E(B-V)_\mathrm{gas}=0.16^{+0.10}_{-0.11}$ from \hb/\hg, electron density $n_e = 570^{+510}_{-290}$ cm$^{-3}$ from the [O II] doublet ratio, electron temperature $T_e = 17000^{+1500}_{-1500}$ K from the [O III] $\lambda4363$/ [O III] $\lambda5007$ ratio, and an ionization parameter $\log(U)=-2.18^{+0.03}_{-0.03}$ from the [O III]/[O II] ratio. Using a direct $T_e$ method, we calculate an oxygen abundance $12+\log\mathrm{(O/H)}=7.67\pm0.08$ and the carbon-to-oxygen (C/O) abundance ratio $\log\mathrm{(C/O)}=-0.87^{+0.13}_{-0.10}$. This C/O ratio is smaller than compared to $z=0$ and $z=2$ - 4 star-forming galaxies, albeit with moderate significance. This indicates the reionization-era galaxies might be undergoing a rapid build-up of stellar mass with high specific star-formation rates. A UV diagnostic based on the ratios of C III] $λ\lambda1907,1909$/He II $\lambda1640$ versus O III] $\lambda1666$/He II $\lambda1640$ suggests that the star formation is the dominant source of ionization, similar to the local extreme dwarf galaxies and $z\sim2$ - 4 He II-detected galaxies. The [O III]/[O II] and C IV/C III] ratios of the composite spectrum are marginally larger than the criteria used to select galaxies as LyC leakers, suggesting that some of the galaxies in our sample are strong contributors to the reionizing radiation.

astro-ph.GA↗

arXiv2024

Deciphering Lyman-$α$ Emission Deep into the Epoch of Reionisation

During the epoch of reionisation the first galaxies were enshrouded in pristine neutral gas, with one of the brightest emission lines in star-forming galaxies, Lyman-$α$ (Ly$α$), expected to remain undetected until the Universe became ionised. Providing an explanation for the surprising detection of Ly$α$ in these early galaxies is a major challenge for extra-galactic studies. Recent JWST observations have reignited the debate on whether residence in an overdensity of galaxies is a it sufficient and necessary condition for Ly$α$ to escape. Here, we take unique advantage of both high-resolution and high-sensitivity images from the JWST instrument NIRCam to reveal that all galaxies in a sample of z>7 Ly$α$ emitters have close companions. We exploit novel on-the-fly radiative transfer magnetohydrodynamical simulations with cosmic ray feedback to show that galaxies with frequent mergers have very bursty star formation which drives episodes of high intrinsic Ly$α$ emission and facilitates the escape of Ly$α$ photons along channels cleared of neutral gas. We conclude that the rapid build up of stellar mass through mergers presents a compelling solution to the long-standing puzzle of the detection of Ly$α$ emission deep into the epoch of reionisation.

astro-ph.GA↗

arXiv2023

A Milky Way-like barred spiral galaxy at a redshift of 3

The majority of massive disk galaxies in the local Universe show a stellar barred structure in their central regions, including our Milky Way. Bars are supposed to develop in dynamically cold stellar disks at low redshift, as the strong gas turbulence typical of disk galaxies at high redshift suppresses or delays bar formation. Moreover, simulations predict bars to be almost absent beyond $z = 1.5$ in the progenitors of Milky Way-like galaxies. Here we report observations of ceers-2112, a barred spiral galaxy at redshift $z_{\rm phot} \sim 3$, which was already mature when the Universe was only 2 Gyr old. The stellar mass ($M_{\star} = 3.9 \times 10^9 M_{\odot}$) and barred morphology mean that ceers-2112 can be considered a progenitor of the Milky Way, in terms of both structure and mass-assembly history in the first 2 Gyr of the Universe, and was the closest in mass in the first 4 Gyr. We infer that baryons in galaxies could have already dominated over dark matter at $z \sim 3$, that high-redshift bars could form in approximately 400 Myr and that dynamically cold stellar disks could have been in place by redshift $z = 4-5$ (more than 12 Gyrs ago).

astro-ph.GA↗

arXiv2023

CEERS: MIRI deciphers the spatial distribution of dust-obscured star formation in galaxies at $0.1<z<2.5$

[Abridged] We combined HST images from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey with JWST images from the Cosmic Evolution Early Release Science (CEERS) survey to measure the stellar and dust-obscured star formation distributions of a mass-complete ($>10^{10}M_\odot$) sample of 69 star-forming galaxies (SFGs) at $0.1 75$; 35 galaxies). At lower $S/N$, simulations show that simultaneous measurements of the size and Sérsic index become unreliable. We extended our study to fainter sources ($S/N>10$; 69 galaxies) by fixing their Sérsic index to unity. The Sérsic index of bright galaxies ($S/N>75$) has a median value of 0.7, which, together with their axis ratio distribution, suggests a disk-like morphology in the rest-MIR. Galaxies above the main sequence (MS; i.e., starbursts) have rest-MIR sizes that are a factor 2 smaller than their rest-optical sizes. The median rest-optical to rest-MIR size ratio of MS galaxies increases with stellar mass, from 1.1 at $10^{9.8}M_\odot$ to 1.6 at $10^{11}M_\odot$. This mass-dependent trend resembles the one found in the literature between the rest-optical and rest-near-infrared sizes of SFGs, suggesting that it is due to radial color gradients affecting rest-optical sizes and that the sizes of the stellar and star-forming components of SFGs are, on average, consistent at all masses. There is, however, a small population of SFGs (15%) with a compact star-forming component embedded in a larger stellar structure. This could be the missing link between galaxies with an extended stellar component and those with a compact stellar component, the so-called blue nuggets.

astro-ph.GA↗

arXiv2023

Cosmic Evolution Early Release Science Survey (CEERS): Multi-classing Galactic Dwarf Stars in the deep JWST/NIRCam

Low mass (sub)stellar objects represent the low end of the initial mass function, the transition to free-floating planets and a prominent interloper population in the search for high-redshift galaxies. Without proper motions or spectroscopy, can one identify these objects photometrically? JWST/NIRCam has several advantages over HST/WFC3 NIR: more filters, a greater wavelength range, and greater spatial resolution. Here, we present a catalogue of (sub)stellar dwarfs identified in the Cosmic Evolution Early Release Science Survey (CEERS). We identify 518 stellar objects down to $m_F200W \sim 28$ using half-light radius, a full three magnitudes deeper than typical HST/WFC3 images. A kNN nearest neighbour algorithm identifies and types these sources, using four HST/WFC3 and four NIRCam filters, trained on SpeX spectra of nearby brown dwarfs. The kNN with four neighbors classifies well within two subtypes: e.g M2$\pm$2 or T4$\pm$2, achieving $\sim$95% precision and recall. More granular typing results in worse metrics. In CEERS, we find 9 M8$\pm$2, 2 L6$\pm$2, 1 T4$\pm$2, and 15 T8$\pm$2. We compare the observed long wavelength NIRCam colours -- not used in the kNN -- to those expected for brown dwarf atmospheric models. The NIRCam F356W-F444W and F410M-F444W colours are redder by a magnitude for the type assigned by the kNN, hinting at a wider variety of atmospheres for these objects. We find a 300-350pc scale-height for M6$\pm$2 dwarfs plus a second structural component and a 150-200pc scale-height for T6$\pm$2 type dwarfs, consistent with literature values.

astro-ph.GA↗

arXiv2023

JWST CEERS probes the role of stellar mass and morphology in obscuring galaxies

In recent years, observations have uncovered a population of massive galaxies that are invisible or very faint in deep optical/near-infrared (near-IR) surveys but brighter at longer wavelengths. However, the nature of these optically dark or faint galaxies (OFGs; one of several names given to these objects) is highly uncertain. In this work, we investigate the drivers of dust attenuation in the JWST era. In particular, we study the role of stellar mass, size, and orientation in obscuring star-forming galaxies (SFGs) at $3 < z < 7.5$, focusing on the question of why OFGs and similar galaxies are so faint at optical/near-IR wavelengths. We find that stellar mass is the primary proxy for dust attenuation, among the properties studied. Effective radius and axis ratio do not show a clear link with dust attenuation, with the effect of orientation being close to random. However, there is a subset of highly dust attenuated ($A_V > 1$, typically) SFGs, of which OFGs are a specific case. For this subset, we find that the key distinctive feature is their compact size (for massive systems with $\log (M_{*}/M_{\odot}) > 10$); OFGs exhibit a 30% smaller effective radius than the average SFG at the same stellar mass and redshift. On the contrary, OFGs do not exhibit a preference for low axis ratios (i.e., edge-on disks). The results in this work show that stellar mass is the primary proxy for dust attenuation and compact stellar light profiles behind the thick dust columns obscuring typical massive SFGs.

astro-ph.GA↗

arXiv2023

A CEERS Discovery of an Accreting Supermassive Black Hole 570 Myr after the Big Bang: Identifying a Progenitor of Massive z > 6 Quasars

We report the discovery of an accreting supermassive black hole at z=8.679, in CEERS_1019, a galaxy previously discovered via a Ly$α$-break by Hubble and with a Ly$α$ redshift from Keck. As part of the Cosmic Evolution Early Release Science (CEERS) survey, we observed this source with JWST/NIRSpec spectroscopy, MIRI and NIRCam imaging, and NIRCam/WFSS slitless spectroscopy. The NIRSpec spectra uncover many emission lines, and the strong [O III] emission line confirms the ground-based Ly$α$ redshift. We detect a significant broad (FWHM~1200 km/s) component in the H$β$ emission line, which we conclude originates in the broad-line region of an active galactic nucleus (AGN), as the lack of a broad component in the forbidden lines rejects an outflow origin. This hypothesis is supported by the presence of high-ionization lines, as well as a spatial point-source component embedded within a smoother surface brightness profile. The mass of the black hole is log($M_{BH}/M_{\odot})=6.95{\pm}0.37$, and we estimate that it is accreting at 1.2 ($\pm$0.5) x the Eddington limit. The 1-8 $μ$m photometric spectral energy distribution (SED) from NIRCam and MIRI shows a continuum dominated by starlight and constrains the host galaxy to be massive (log M/M$_{\odot}$~9.5) and highly star-forming (SFR~30 M$_{\odot}$ yr$^{-1}$). Ratios of the strong emission lines show that the gas in this galaxy is metal-poor (Z/Z$_{\odot}$~0.1), dense (n$_{e}$~10$^{3}$ cm$^{-3}$), and highly ionized (log U~-2.1), consistent with the general galaxy population observed with JWST at high redshifts. We use this presently highest-redshift AGN discovery to place constraints on black hole seeding models and find that a combination of either super-Eddington accretion from stellar seeds or Eddington accretion from massive black hole seeds is required to form this object by the observed epoch.

astro-ph.GA↗

arXiv2023

Confirmation and refutation of very luminous galaxies in the early universe

During the first 500 million years of cosmic history, the first stars and galaxies formed, seeding the Universe with heavy elements and eventually reionizing the intergalactic medium. Observations with JWST have uncovered a surprisingly high abundance of candidates for early star-forming galaxies, with distances (redshifts, $z$), estimated from multi-band photometry, as large as $z\approx 16$, far beyond pre-JWST limits. While generally robust, such photometric redshifts can suffer from degeneracies and occasionally catastrophic errors. Spectroscopic measurement is required to validate these sources and to reliably quantify physical properties that can constrain galaxy formation models and cosmology. Here we present JWST spectroscopy that confirms redshifts for two very luminous galaxies with $z > 11$, but also demonstrates that another candidate with suggested $z\approx 16$ instead has $z = 4.9$, with an unusual combination of nebular line emission and dust reddening that mimics the colors expected for much more distant objects. These results reinforce evidence for the early, rapid formation of remarkably luminous galaxies, while also highlighting the necessity of spectroscopic verification. The large abundance of bright, early galaxies may indicate shortcomings in current galaxy formation models, or deviation from physical properties (such as the stellar initial mass function) that are generally believed to hold at later times.

astro-ph.GA↗

arXiv2023

GA-NIFS: Black hole and host galaxy properties of two z$\simeq$6.8 quasars from the NIRSpec IFU

Integral Field Spectroscopy (IFS) with JWST NIRSpec will significantly improve our understanding of the first quasars, by providing spatially resolved, infrared spectroscopic capabilities which cover key rest-frame optical emission lines that have been previously unobservable. Here we present our results from the first two z>6 quasars observed as a part of the Galaxy Assembly with NIRSpec IFS (GA-NIFS) GTO program, DELS J0411-0907 at z=6.82 and VDES J0020-3653 at z=6.86. By observing the H$β$, [OIII], and H$α$ emission lines in these high-z quasars for the first time, we measure accurate black hole masses, $M_{\rm{BH}}=1.85e9$ and $2.9e9$M$_\odot$, corresponding to Eddington ratios of $λ_{\rm{Edd}}=0.8$ and 0.4 for DELS J0411-0907 and VDES J0020-3653 respectively. These provide a key comparison for existing estimates from the more uncertain MgII line. We perform quasar-host decomposition using models of the quasars' broad lines to measure the underlying host galaxies. We also discover multiple emission line regions surrounding each of the host galaxies, which are likely companion galaxies undergoing mergers with these hosts. We measure the star formation rates, excitation mechanisms, and dynamical masses of the hosts and companions, measuring the $M_{\rm{BH}}/M_{\rm{dyn}}$ ratios at high-z using these estimators for the first time. DELS J0411-0907 and VDES J0020-3653 both lie above the local black hole--host mass relation, and are consistent with the existing observations of $z\gtrsim6$ quasar host galaxies with ALMA. We detect ionized outflows in [OIII] and H$β$ from both quasars, with mass outflow rates of 58 and 525 M$_{\odot}$/yr for DELS J0411-0907 and VDES J0020-3653, much larger than their host star formation rates of <33 and <54 M$_\odot$/yr. This work highlights the exceptional capabilities of the JWST NIRSpec IFU for observing quasars in the early Universe.

astro-ph.GA↗

arXiv2023

ALMA FIR View of Ultra High-redshift Galaxy Candidates at $z\sim$ 11-17: Blue Monsters or Low-$z$ Red Interlopers?

We present ALMA Band~7 observations of a remarkably bright galaxy candidate at $z_{\rm phot}$=$16.7^{+1.9}_{-0.3}$ ($M_{\rm UV}$=$-21.6$), S5-z17-1, identified in JWST Early Release Observation data of Stephen's Quintet. We do not detect the dust continuum at 866~$μ$m, ruling out the possibility that \targb\ is a low-$z$ dusty starburst with a star-formation rate of $\gtrsim 30$~$M_{\odot}$~yr$^{-1}$. We detect a 5.1$σ$ line feature at $338.726\pm0.007$~GHz exactly coinciding with the JWST source position, with a 2\% likelihood of the signal being spurious. The most likely line identification would be [OIII]52$μ$m at $z=16.01$ or [CII]158$μ$m at $z=4.61$, whose line luminosities do not violate the non-detection of the dust continuum in both cases. Together with three other $z\gtrsim$ 11--13 candidate galaxies recently observed with ALMA, we conduct a joint ALMA and JWST spectral energy distribution (SED) analysis and find that the high-$z$ solution at $z\sim$11--17 is favored in every candidate as a very blue (UV continuum slope of $\simeq-2.3$) and luminous ($M_{\rm UV}\simeq[-$24:$-21]$) system. Still, we find in several candidates that reasonable SED fits ($Δ$ $χ^{2}\lesssim4$) are reproduced by type-II quasar and/or quiescent galaxy templates with strong emission lines at $z\sim3$--5, where such populations predicted from their luminosity functions and EW([OIII]+H$β$) distributions are abundant in survey volumes used for the identification of the $z\sim$11--17 candidates. While these recent ALMA observation results have strengthened the likelihood of the high-$z$ solutions, lower-$z$ possibilities are not completely ruled out in several of the $z\sim$11--17 candidates, indicating the need to consider the relative surface densities of the lower-$z$ contaminants in the ultra high-$z$ galaxy search.

astro-ph.GA↗

arXiv2023

Spectroscopic Confirmation of CEERS NIRCam-selected Galaxies at $\boldsymbol{z \simeq 8-10}$

We present JWST/NIRSpec prism spectroscopy of seven galaxies selected from the Cosmic Evolution Early Release Science Survey (CEERS) NIRCam imaging with photometric redshifts z_phot>8. We measure emission line redshifts of z=7.65 and 8.64 for two galaxies, and z=9.77(+0.37,-0.29) and 10.01(+0.14,-0.19) for two others via the detection of continuum breaks consistent with Lyman-alpha opacity from a mostly neutral intergalactic medium. The presence (absense) of strong breaks (strong emission lines) give high confidence that these two galaxies are at z>9.6, but the break-derived redshifts have large uncertainties given the low spectral resolution and relatively low signal-to-noise of the CEERS NIRSpec prism data. The two z~10 sources are relatively luminous (M_UV<-20), with blue continua (-2.3 8 candidates with CEERS NIRSpec spectroscopy do not have secure redshifts, but the absence of emission lines in their spectra is consistent with redshifts z>9.6. We find that z>8 photometric redshifts are generally in agreement (within uncertainties) with the spectroscopic values. However, the photometric redshifts tend to be slightly overestimated (average Delta(z)=0.50+/-0.12), suggesting that current templates do not fully describe the spectra of very high-z sources. Overall, our results solidifies photometric evidence for a high space density of bright galaxies at z>8 compared to theoretical model predictions, and further disfavors an accelerated decline in the integrated UV luminosity density at z>8.

astro-ph.GA↗

arXiv2023

GA-NIFS: A massive black hole in a low-metallicity AGN at $z\sim5.55$ revealed by JWST/NIRSpec IFS

We present JWST/NIRSpec Integral Field Spectrograph rest-frame optical data of the compact $z=5.55$ galaxy GS_3073. Its prominent broad components in several hydrogen and helium lines (while absent in the forbidden lines), and the detection of a large equivalent width of He II$\lambda4686$, EW(He II) ~ 20A, unambiguously identify it as an active galactic nucleus (AGN). We measure a gas-phase metallicity of $Z_{\rm gas}/Z_\odot\sim0.21^{+0.08}_{-0.04}$, lower than what has been inferred for both more luminous AGN at similar redshift and lower redshift AGN. We empirically show that classical emission line ratio diagnostic diagrams cannot be used to distinguish between the primary ionisation source (AGN or star formation) for such low-metallicity systems, whereas different diagnostic diagrams involving He II$\lambda4686$ prove very useful, independent of metallicity. We measure the central black hole mass to be $\log(M_{\rm BH}/M_\odot)\sim8.2\pm0.4$ based on the luminosity and width of the broad line region of the H$α$ emission. While this places GS_3073 at the lower end of known high-redshift black hole masses, it still appears to be over-massive compared to its host galaxy properties. We detect an outflow with projected velocity $\gtrsim700$ km/s and infer an ionised gas mass outflow rate of about $100\ M_\odot/$yr, suggesting that GS_3073 is able to enrich the intergalactic medium with metals one billion years after the Big Bang.

astro-ph.GA↗

arXiv2023

A z=1.85 galaxy group in CEERS: evolved, dustless, massive intra-halo light and a brightest group galaxy in the making

We present CEERS JWST/NIRCam imaging of a massive galaxy group at z=1.85, to explore the early JWST view on massive group formation in the distant Universe. The group contains >16 members (including 6 spectros. confirmations) down to log10(Mstar/Msun)=8.5, including the brightest group galaxy (BGG) in the process of actively assembling at this redshift. The BGG is comprised of multiple merging components extending ~3.6" (30kpc) across the sky. The BGG contributes 69% of the group's total galactic stellar mass, with one of the merging components containing 76% of the total mass of the BGG and a SFR>1810Msun/yr. Most importantly, we detect intra-halo light (IHL) in several HST and JWST/NIRCam bands, allowing us to construct a state-of-the-art rest-frame UV-NIR Spectral Energy Distribution of the IHL for the first time at this high redshift. This allows stellar population characterisation of both the IHL and member galaxies, as well as the morphology distribution of group galaxies vs. their star-formation activity when coupled with Herschel data. We create a stacked image of the IHL, giving us a sensitivity to extended emission of 28.5 mag/arcsec2 at rest-frame 1um. We find that the IHL is extremely dust poor (Av~0), containing an evolved stellar population of log10(t50/yr)=8.8, corresponding to a formation epoch for 50% of the stellar material 0.63Gyr before z=1.85. There is no evidence of ongoing star-formation in the IHL. The IHL in this group at z=1.85 contributes ~10% of the total stellar mass, comparable with what is observed in local clusters. This suggests that the evolution of the IHL fraction is more self-similar with redshift than predicted by some models, challenging our understanding of IHL formation during the assembly of high-redshift clusters. JWST is unveiling a new side of group formation at this redshift, which will evolve into Virgo-like structures in the local Universe.

astro-ph.GA↗