arXiv subjects

Irene Shivaei

Publications and source records attributed to Irene Shivaei.

At least 73 records · Page 4Linked to original sources

arXiv2024

A High-resolution Far-infrared Survey to Probe Black Hole-Galaxy Co-evolution

Far-infrared (FIR) surveys are critical to probing the co-evolution of black holes and galaxies, since of order half the light from accreting black holes and active star formation is emitted in the rest-frame infrared over $0.5\lesssim z \lesssim 10$. For deep fields with areas of 1 deg$^2$ or less, like the legacy surveys GOODS, COSMOS, and CANDELS, source crowding means that sub-arcsecond resolution is essential. In this paper, we show with a simulation of the FIR sky that observations made with a small telescope (2 m) at low angular resolution preferentially detect the brightest galaxies, and we demonstrate the scientific value of a space mission that would offer sub-arcsecond resolution. We envisage a facility that would provide high-resolution imaging and spectroscopy over the wavelength range $25-400\,μm$, and we present predictions for an extragalactic survey covering $0.5\,\hbox{deg}^2$. Such a survey is expected to detect tens of thousands of star-forming galaxies and thousands of Active Galactic Nuclei (AGN), in multiple FIR lines (e.g. [CII], [OI], [CI]) and continuum. At the longest wavelengths (200-400$\,μ$m), it would probe beyond the reionization epoch, up to $z\sim 7$-8. A combination of spectral resolution, line sensitivity, and broad spectral coverage would allow us to learn about the physical conditions (temperature, density, metallicity) characterizing the interstellar medium of galaxies over the past $\sim 12$ billion years and to investigate galaxy-AGN co-evolution.

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arXiv2024

An unambiguous AGN and a Balmer break in an Ultraluminous Little Red Dot at z=4.47 from Ultradeep UNCOVER and All the Little Things Spectroscopy

We present a detailed exploration of the most optically-luminous Little Red Dot ($L_{Hα}=10^{44}$erg/s, $L_V=10^{45}$erg/s, F444W=22AB) found to date. Located in the Abell 2744 field, source A744-45924 was observed by NIRSpec/PRISM with ultradeep spectroscopy reaching SNR$\sim$100pix$^{-1}$, high-resolution 3-4 micron NIRCam/Grism spectroscopy, and NIRCam Medium Band imaging. The NIRCam spectra reveal high rest-frame EW $W_{Hα,0,broad}>800$Å, broad H$α$ emission (FWHM$\sim$4500 km/s), on top of narrow, complex absorption. NIRSpec data show exceptionally strong rest-frame UV to NIR Fe II emission ($W_{FeII-UV,0}\sim$340Å), N IV]$λλ$1483,1486 and N III]$λ$1750, and broad NIR O I $λ$8446 emission. The spectra unambiguously demonstrate a broad-line region associated with an inferred $M_{BH}\sim10^9M_\odot$ supermassive black hole embedded in dense gas, which might explain a non-detection in ultradeep Chandra X-ray data (>$10\times$ underluminous relative to broad $L_{Hα}$). Strong UV Nitrogen lines suggest supersolar N/O ratios due to rapid star formation or intense radiation near the AGN. The continuum shows a clear Balmer break at rest-frame 3650Å, which cannot be accounted for by an AGN power-law alone. A stellar population model produces an excellent fit with a reddened Balmer break and implying a massive ($M_*\sim8\times10^{10}M_\odot$), old $\sim$500 Myr, compact stellar core, among the densest stellar systems known ($ρ\sim3\times10^6M_\odot$/pc$^2$ for $R_{e,opt}=70\pm10$ pc), and AGN emission with extreme intrinsic EW $W_{Hα,0}\gg$1000Å. However, although high $M_*$ and $M_{BH}$ are supported by evidence of an overdensity containing 40 galaxies at $z=4.41-4.51$, deep high-resolution spectroscopy is required to confirm stellar absorption and rule out that dense gas around the AGN causes the Balmer break instead.

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arXiv2024

JADES: Primaeval Lyman-$\mathrmα$ emitting galaxies reveal early sites of reionisation out to redshift $z \sim 9$

$\require{mediawiki-texvc}$Given the sensitivity of the resonant Lyman-$\mathrmα$ (Ly$\mathrmα$) transition to absorption by neutral hydrogen, observations of Ly$\mathrmα$ emitting galaxies (LAEs) have been widely used to probe the ionising capabilities of reionisation-era galaxies and their impact on the intergalactic medium (IGM). However, prior to JWST our understanding of the contribution of fainter sources and of ionised `bubbles' at earlier stages of reionisation remained uncertain. Here, we present the characterisation of three exceptionally distant LAEs at $z>8$, newly discovered by JWST/NIRSpec in the JADES survey. These three similarly bright ($M_\text{UV} \approx -20\,\mathrm{mag}$) LAEs exhibit small Ly$\mathrmα$ velocity offsets from the systemic redshift, $Δv_\mathrm{Lyα} \lesssim 200\,\mathrm{km\,s^{-1}}$, yet span a range of Ly$\mathrmα$ equivalent widths ($15\,Å$, $31\,Å$, and $132\,Å$). The former two show moderate Ly$\mathrmα$ escape fractions ($f_\mathrm{esc,Lyα} \approx 10\%$), whereas Ly$\mathrmα$ escapes remarkably efficiently from the third ($f_\mathrm{esc,Lyα} \approx 72\%$), which moreover is very compact (half-light radius of $90\pm10\,\mathrm{pc}$). We find these LAEs are low-mass galaxies dominated by very recent, vigorous bursts of star formation accompanied by strong nebular emission from metal-poor gas. We infer the two LAEs with modest $f_\mathrm{esc,Lyα}$, one of which reveals evidence for ionisation by an active galactic nucleus, may have reasonably produced small ionised bubbles preventing complete IGM absorption of Ly$\mathrmα$. The third, however, requires a $\sim 3\,\text{physical Mpc}$ bubble, indicating faint galaxies have contributed significantly. The most distant LAEs thus continue to be powerful observational probes into the earlier stages of reionisation.

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arXiv2024

No evidence for a significant evolution of $M_{\bullet}$-$M_*$ relation in massive galaxies up to z$\sim$4

Over the past two decades, tight correlations between black hole masses ($M_\bullet$) and their host galaxy properties have been firmly established for massive galaxies ($\log(M_*/M_{\odot})\gtrsim10$) at low-$z$ ($z<1$), indicating coevolution of supermassive black holes and galaxies. However, the situation at high-$z$, especially beyond cosmic noon ($z\gtrsim2.5$), is controversial. With a combination of \emph{JWST} NIRCam/wide field slitless spectroscopy (WFSS) from FRESCO, CONGRESS and deep multi-band NIRCam/image data from JADES in the GOODS fields, we study the black hole to galaxy mass relation at z$\sim$1--4. After identifying 18 broad-line active galactic nuclei (BL AGNs) at $1 2.5$) from the WFSS data, we measure their black hole masses based on broad near-infrared lines (Pa $α$, Pa $β$, and He\,I $λ$10833\,Å), and constrain their stellar masses ($M_{*}$) from AGN-galaxy image decomposition or SED decomposition. Taking account of the observational biases, the intrinsic scatter of the $M_{\bullet}-M_{*}$ relation, and the errors in mass measurements, we find no significant difference in the $M_{\bullet}/M_{*}$ ratio for 2.5 $< $ z $ <$ 4 compared to that at lower redshifts ($1 < z < 2.5$), suggesting no evolution of the $M_{\bullet} - M_{*}$ relation at $\log(M_*/M_{\odot})\gtrsim10$ up to z$\sim$4.

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arXiv2024

The Relation between AGN and Host Galaxy Properties in the JWST Era: I. Seyferts at Cosmic Noon are Obscured and Disturbed

The morphology of a galaxy reflects the mix of physical processes occurring within and around it, offering indirect clues to its formation and evolution. We apply both visual classification and computer vision to test the suspected connection between galaxy mergers and AGN activity, as evidenced by a close/merging galaxy pair, or tidal features surrounding an apparently singular system. We use JADES JWST/NIRCam imagery of a complete, mutliwavelength AGN sample recently expanded with JWST/MIRI photometry. This 0.9-25 $μ$m dataset enables constraints on the host galaxy morphologies of a broad range of AGN beyond z$\sim$1, including heavily obscured examples missing from previous studies. Our primary AGN sample consists of 243 lightly to highly obscured X-ray-selected AGN and 138 presumed Compton-thick, mid-infrared-bright/X-ray-faint AGN revealed by MIRI. Utilizing the shape asymmetry morphology indicator, $A_S$, as the metric for disturbance, we find that 88% of the Seyferts sampled are strongly spatially disturbed ($A_S>0.2$). The experimental design we employ reveals a $\gtrsim 3σ$ obscuration-merger ($N_H$-$A_S$) correlation at $0.6<z<2.4$, and also recovers a physical distinction between the X-ray- and mid-IR-detected AGN suggestive of their link to a common evolutionary scenario. Placing the observed pattern of disturbances in the context of the other average host galaxy properties, we conclude that mergers are common amongst obscured AGN. This finding presents tension with the leading model on AGN fueling that requires Seyfert AGN with sub-quasar luminosities ($L_{bol} < 10^{45}$ ergs/s) to evolve only through non-merger mechanisms.

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arXiv2024

Extreme emission line galaxies detected in JADES JWST/NIRSpec I: inferred galaxy properties

Extreme emission line galaxies (EELGs) exhibit large equivalent widths (EW) in their rest-optical emission lines ([OIII]$\lambda5007$ or H$α$ rest-frame EW$ > 750Å$) which can be tied to a recent upturn in star formation rate, due to the sensitivity of the nebular line emission and the rest-optical continuum to young ($<10$Myr) and evolved stellar populations, respectively. By studying a sample of 85 star forming galaxies (SFGs), spanning the redshift and magnitude interval $3 $ M$_{UV}>-21$, in the JWST Advanced Deep Extragalactic Survey (JADES) with NIRSpec/prism spectroscopy, we determine that SFGs initiate an EELG phase when entering a significant burst of star formation, with the highest EWs observed in EELGs with the youngest luminosity-weighted ages ($<5$ Myr old) and the highest burst intensity (those with the greatest excess between their current and long-term average SFR). We spectroscopically confirm that a greater proportion of SFGs are in an EELG phase at high redshift in our UV-selected sample ($61\pm4\%$ in our $z>5.7$ high-redshift bin, compared to $23^{+4}_{-1}\%$ in our lowest-redshift bin $3 5.7$ have observed Lyman-$α$ emission, potentially lying within large ionised regions. The high detection rate of Lyman-$α$ emitters in our EELG selection suggests that the physical conditions associated with entering an EELG phase also promote the escape of Lyman-$α$ photons.

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arXiv2024

Dynamics of Star-forming Galaxies in a Massive Structure at \lowercase{$z\sim$} 2.2: Evidence for Galaxy Harassment in high-$z$ Environments

We spectroscopically confirm a new protocluster in the COSMOS field at $z$=2.24430 with Keck/MOSFIRE, dubbed CC2.2B, which is in the immediate vicinity of CC2.2A protocluster, originally presented in \cite{Darvish20}. CC2.2B and CC2.2A centroids are separated by $\sim$5.5 Mpc(angular) and $\sim$16 comoving Mpc(radial). CC2.2B and CC2.2A have similar properties, with CC2.2B having a line-of-sight velocity dispersion and estimated total mass of $σ_{los}$=693$\pm$65 km s$^{-1}$ and $M_{total}$=($\sim$2-3)$\times$10$^{14}$ $M_{\odot}$, respectively. These two similar overdensities are likely still in the merging process and will likely collapse into a more massive structure at lower redshifts. We combine CC2.2A and CC2.2B data to investigate the role of high-$z$ protocluster environments on the dynamics of star-forming (SF) galaxies compared to a similarly selected field sample. We find that on average, protocluster SF galaxies have $\sim$0.1 dex (at $\sim$1.8$σ$ significance) lower gas velocity dispersions, $\sim$0.2 dex (at $\sim$2.2$σ$ significance) lower dynamical masses, and $\sim$0.2 dex lower dynamical-to-stellar mass ratio than the field SF galaxies. We argue that galaxy harassment and galaxy-galaxy interactions can potentially explain these differences. We also find a factor of $\sim$2-3 lower scatter around the mean $σ$-$M_{*}$, $M_{dyn}$-$M_{*}$, and $M_{dyn}$/$M_{*}$ vs. $M_{*}$ relations for protocluster SF galaxies than the field. This could be due to a more uniform formation for protocluster galaxies than their field counterparts. Our results have potential implications for the physics of preprocessing in early environments.

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arXiv2024

Application of Manifold Learning to Selection of Different Galaxy Populations and Scaling Relation Analysis

The growing volume of data produced by large astronomical surveys necessitates the development of efficient analysis techniques capable of effectively managing high-dimensional datasets. This study addresses this need by demonstrating some applications of manifold learning and dimensionality reduction techniques, specifically the Self-Organizing Map (SOM), on the optical+NIR SED space of galaxies, with a focus on sample comparison, selection biases, and predictive power using a small subset. To this end, we utilize a large photometric sample from the five CANDELS fields and a subset with spectroscopic measurements from the KECK MOSDEF survey in two redshift bins at $z\sim1.5$ and $z\sim2.2$. We trained SOM with the photometric data and mapped the spectroscopic data onto it as our study case. We found that MOSDEF targets do not cover all SED shapes existing in the SOM. Our findings reveal that Active Galactic Nuclei (AGN) within the MOSDEF sample are mapped onto the more massive regions of the SOM, confirming previous studies and known selection biases towards higher-mass, less dusty galaxies. Furthermore, SOM were utilized to map measured spectroscopic features, examining the relationship between metallicity variations and galaxy mass. Our analysis confirmed that more massive galaxies exhibit lower [OIII]/H$β$ and [OIII]/[OII] ratios and higher H$α$/H$β$ ratios, consistent with the known mass-metallicity relation. These findings highlight the effectiveness of SOM in analyzing and visualizing complex, multi-dimensional datasets, emphasizing their potential in data-driven astronomical studies.

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arXiv2024

JADES + JEMS: A Detailed Look at the Buildup of Central Stellar Cores and Suppression of Star Formation in Galaxies at Redshifts 3 < z < 4.5

We present a spatially resolved study of stellar populations in 6 galaxies with stellar masses $M_*\sim10^{10}M_\odot$ at $z\sim3.7$ using 14-filter JWST/NIRCam imaging from the JADES and JEMS surveys. The 6 galaxies are visually selected to have clumpy substructures with distinct colors over rest-frame $3600-4100Å$, including a red, dominant stellar core that is close to their stellar-light centroids. With 23-filter photometry from HST to JWST, we measure the stellar-population properties of individual structural components via SED fitting using Prospector. We find that the central stellar cores are $\gtrsim2$ times more massive than the Toomre mass, indicating they may not form via single in-situ fragmentation. The stellar cores have stellar ages of $0.4-0.7$ Gyr that are similar to the timescale of clump inward migration due to dynamical friction, suggesting that they likely instead formed through the coalescence of giant stellar clumps. While they have not yet quenched, the 6 galaxies are below the star-forming main sequence by $0.2-0.7$ dex. Within each galaxy, we find that the specific star formation rate is lower in the central stellar core, and the stellar-mass surface density of the core is already similar to quenched galaxies of the same masses and redshifts. Meanwhile, the stellar ages of the cores are either comparable to or younger than the extended, smooth parts of the galaxies. Our findings are consistent with model predictions of the gas-rich compaction scenario for the buildup of galaxies' central regions at high redshifts. We are likely witnessing the coeval formation of dense central cores, along with the onset of galaxy-wide quenching at $z>3$.

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arXiv2024

All the Little Things in Abell 2744: $>$1000 Gravitationally Lensed Dwarf Galaxies at $z=0-9$ from JWST NIRCam Grism Spectroscopy

Dwarf galaxies hold the key to crucial frontiers of astrophysics, however, their faintness renders spectroscopy challenging. Here we present the JWST Cycle 2 survey, All the Little Things (ALT, PID 3516), which is designed to seek late-forming Pop III stars and the drivers of reionization at $z\sim6-7$. ALT has acquired the deepest NIRCam grism spectroscopy yet (7-27 hr), at JWST's most sensitive wavelengths (3-4 $μ$m), covering the powerful lensing cluster Abell 2744. Over the same 30 arcmin$^2$, ALT's ultra-deep F070W+F090W imaging ($\sim$30 mag) enables selection of very faint sources at $z>6$. We demonstrate the success of ALT's novel ``butterfly" mosaic to solve spectral confusion and contamination, and introduce the ``Allegro" method for emission line identification. By collecting spectra for every source in the field of view, ALT has measured precise ($R\sim1600$) redshifts for 1630 sources at $z=0.2-8.5$. This includes one of the largest samples of distant dwarf galaxies: [1015, 475, 50] sources less massive than the SMC, Fornax, and Sculptor with $\log(M_{*}/M_{\odot})<$[8.5, 7.5, 6.5]. We showcase ALT's discovery space with: (i) spatially resolved spectra of lensed clumps in galaxies as faint as $M_{\rm{UV}}\sim-15$; (ii) large-scale clustering -- overdensities at $z$=[2.50, 2.58, 3.97, 4.30, 5.66, 5.77, 6.33] hosting massive galaxies with striking Balmer breaks; (iii) small-scale clustering -- a system of satellites around a Milky Way analog at $z\sim6$; (iv) spectroscopically confirmed multiple images that help constrain the lensing model underlying all science in this legacy field; (v) sensitive star-formation maps based on dust-insensitive tracers such as Pa$α$; (vi) direct spectroscopic discovery of rare sources such as AGN with ionized outflows. These results provide a powerful proof of concept for how grism surveys maximize the potential of strong lensing fields.

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arXiv2024

Stacking and Analyzing $z\approx 2$ MOSDEF Galaxies by Spectral Types: Implications for Dust Geometry and Galaxy Evolution

We examine star-formation and dust properties for a sample of 660 galaxies at $1.37\leq z\leq 2.61$ in the MOSDEF survey by dividing them into groups with similarly-shaped spectral energy distributions (SEDs). For each group, we combine the galaxy photometry into a finely-sampled composite SED, and stack their spectra. This method enables the study of more complete galaxy samples, including galaxies with very faint emission lines. We fit these composite SEDs with Prospector to measure the stellar attenuation and SED-based star-formation rates (SFRs). We also derive emission-line properties from the spectral stacks, including Balmer decrements, dust-corrected SFRs, and metallicities. We find that stellar attenuation correlates most strongly with mass, while nebular attenuation correlates strongly with both mass and SFR. Furthermore, the excess of nebular compared to stellar attenuation correlates most strongly with SFR. The highest SFR group has 2 mag of excess nebular attenuation. Our results are consistent with a model in which star-forming regions become more dusty as galaxy mass increases. To explain the increasing excess nebular attenuation, we require a progressively larger fraction of star formation to occur in highly-obscured regions with increasing SFR. This highly-obscured star formation could occur in dusty clumps or central starbursts. Additionally, as each galaxy group represents a different evolutionary stage, we study their locations on the UVJ and SFR-mass diagrams. As mass increases, metallicity and dust attenuation increase, while sSFR decreases. However, the most massive group moves towards the quiescent region of the UVJ diagram, while showing less obscuration, potentially indicating removal of dust.

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arXiv2024

Extended hot dust emission around the earliest massive quiescent galaxy

A major unsolved problem in galaxy evolution is the early appearance of massive quiescent galaxies that no longer actively form stars only $ \sim 1$ billion years after the Big Bang. Their high stellar masses and extremely compact structure indicate that they formed through rapid bursts of star formation between redshift $z \sim 6-11$. Theoretical models of galaxy evolution cannot explain their high number density, rapid growth and truncation of star formation at such early times, which likely requires extreme feedback to destroy the cold interstellar medium (the fuel for star formation). We report the discovery of a significant reservoir of hot dust in one of the most distant known examples at $z = 4.658$, GS-9209. The dust was identified using JWST's Mid-Infrared Instrument (MIRI), whose unprecedented sensitivity and high spatial resolution, for the first time, firmly show that this dust is significantly more extended than the stars by $\gtrsim 3$ times. We find that the dust has preferentially been evacuated or diluted in the galaxy center. Our analysis finds that the extended hot dust emission is consistent with recent heating by a younger and more spatially extended generation of star formation. This reveals that the earliest quiescent galaxies did not form in a single rapid burst; instead, similar to galaxy growth at later times, the center formed first with star formation continuing in an extended envelope. The growth of this galaxy is truncating from the inside out, consistent with central gas depletion from early AGN feedback.

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arXiv2024

Accelerated Formation of Ultra-Massive Galaxies in the First Billion Years

Recent JWST observations have revealed an unexpected abundance of massive galaxy candidates in the early Universe, extending further in redshift and to lower luminosity than what had previously been found by sub-millimeter surveys. These JWST candidates have been interpreted as challenging the $Λ$CDM cosmology, but, so far, they have mostly relied only on rest-frame ultraviolet data and lacked spectroscopic confirmation of their redshifts. Here we report a systematic study of 36 massive dust-obscured galaxies with spectroscopic redshifts between $z_{\rm spec}=5-9$ from the JWST FRESCO survey. We find no tension with the $Λ$CDM model in our sample. However, three ultra-massive galaxies (log$M_{\star}/M_{\odot}$ $\gtrsim11.0$) require an exceptional fraction of 50% of baryons converted into stars -- two to three times higher than even the most efficient galaxies at later epochs. The contribution from an active nucleus is unlikely because of their extended emission. Ultra-massive galaxies account for as much as 17% of the total cosmic star formation rate density at $z\sim5-6$.

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arXiv2024

The tight correlation of PAH and CO emission from z~0-4

Aim: The cold molecular gas mass is one of the crucial, yet challenging parameters in galaxy evolution studies. Here, we introduce a new calibration for estimating molecular gas masses using mid-infrared (MIR) photometry. This topic is timely, as JWST now allows us to detect the MIR emission of typical main-sequence galaxies across a wide range of masses and star formation rates with modest time investments. This Letter highlights the strong synergy between ALMA and JWST for studies of dust and gas at cosmic noon. Methods: We combine a sample of 14 main sequence galaxies at z=1-3 with robust CO detections and multi-band MIR photometry, along with a literature sample at z=0-4 with CO and PAH spectroscopy, to study the relationship between PAH, CO(1-0), and total IR luminosities. PAH luminosities are derived from modeling rest-frame UV to sub-mm data. The new z=1-3 sample extends previous high-z studies to about an order-of-magnitude lower PAH and CO luminosities, into the regime of local starbursts for the first time. Results: The PAH-to-CO luminosity ratio remains constant across a wide range of luminosities, for various galaxy types, and throughout the explored redshift range. In contrast, the PAH-to-IR and CO-to-IR luminosity ratios deviate from a constant value at high L(IR). The intrinsic scatter in the L(PAH)-L'(CO) relation is 0.21 dex, with a median of 1.40, and a power-law slope of $1.07 \pm 0.04$. Both the PAH-IR and CO-IR relations are sub-linear. Given the tight and uniform PAH-CO relation over ~3 orders of magnitude, we provide a recipe to estimate the cold molecular gas mass of galaxies from PAH luminosities, with a PAH-to-molecular gas conversion factor of $α_{\rm PAH7.7} = (3.08 \pm 1.08)(4.3/α_{\rm CO})\,M_{\odot}/L_{\odot}$. This method opens a new window to explore the gas content of galaxies beyond the local Universe using multi-wavelength JWST/MIRI imaging.

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arXiv2024

A new census of dust and polycyclic aromatic hydrocarbons at z=0.7-2 with JWST MIRI

This paper utilizes the JWST MIRI multi-band imaging data from the SMILES survey (5-25micron), complemented with HST and NIRCam photometric and spectroscopic data from the JADES and FRESCO surveys for 443 star-forming (non-AGN) galaxies at z=0.7-2.0 to extend the study of dust and PAH emission to a new mass and SFR parameter space beyond our local universe. We find a strong correlation between the fraction of dust in PAHs (PAH fraction, q_PAH) with stellar mass. Moreover, the PAH fraction behavior as a function of gas-phase metallicity is similar to that at z~0 from previous studies, suggesting a universal relation: q_PAH is constant (~3.4%) above a metallicity of ~ 0.5$Z_{\odot}$ and decreases to <1% at metallicities $<0.3Z_{\odot}$. This indicates that metallicity is a good indicator of the ISM properties that affect the balance between the formation and destruction of PAHs. The lack of a redshift evolution from z~0-2 also implies that above $0.5\,Z_{\odot}$, the PAH emission effectively traces obscured luminosity and the previous locally-calibrated PAH-SFR calibrations remain applicable in this metallicity regime. We observe a strong correlation between obscured UV luminosity fraction (ratio of obscured to total luminosity) and stellar mass. Above the stellar mass of $>5\times 10^9M_{\odot}$, on average, more than half of the emitted luminosity is obscured, while there exists a non-negligible population of lower mass galaxies with >50% obscured fractions. At a fixed mass, the obscured fraction correlates with SFR surface density. This is a result of higher dust covering fractions in galaxies with more compact star forming regions. Similarly, galaxies with high IRX (IR to UV luminosity) at a given mass or UV continuum slope tend to have higher SFR surface density and shallower attenuation curves, owing to their higher effective dust optical depths and more compact star forming regions.

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arXiv2024

A First Look at Spatially Resolved Star Formation at $4.8<z<6.5$ with JWST FRESCO NIRCam Slitless Spectroscopy

We present the first results on the spatial distribution of star formation in 454 star-forming galaxies at $4.8<z<6.5$ using H-Alpha emission-line maps and F444W imaging tracing the stellar continuum from JWST FRESCO NIRCam Slitless Spectroscopy. Star-forming galaxies with stellar masses $6.8\leq$log($M_{*}/\mathrm{M}_{\odot}$)$<11.1$ have positive H-Alpha equivalent width profiles, providing direct evidence for the inside-out growth of galaxies just after the epoch of reionisation. GALFIT is used to calculate half-light radii, $R_{\mathrm{eff}}$ and central surface densities within 1 kiloparsec, $Σ_{1\mathrm{kpc}}$. At a fixed stellar mass of log$(M_{*}/\mathrm{M}_{\odot})=9.5$, $Σ_{1\mathrm{kpc, H}α}$ is $1.04\pm0.05$ times higher than $Σ_{1\mathrm{kpc, C}}$, $R_{\mathrm{eff, H}α}$ is $1.18\pm0.03$ times larger than $R_{\mathrm{eff, C}}$ and both $R_{\mathrm{eff}}$ measurements are less than 1 kiloparsec. These measurements suggest the rapid build-up of compact bulges just after the epoch of reionisation. By comparing to work done at lower redshifts with HST WFC3 Slitless Spectroscopy as part of the 3D-HST ($z=1$) and CLEAR ($z=0.5$) surveys, we find that $R_{\mathrm{eff}}(z)$ evolves at the same pace for H$α$ and the continuum, but $Σ_{1\mathrm{kpc}}(z)$ evolves faster for H$α$. As a function of the Hubble parameter, $\frac{R_{\mathrm{eff, H}α}}{R_{\mathrm{eff, C}}}=1.1h(z)$ and $\frac{Σ_{1\mathrm{kpc,H}α}}{Σ_{1\mathrm{kpc,C}}}=h(z)^{1.3}$. These functions suggest that the inside-out growth of the disk dominates the inside-out growth of the bulge towards lower redshifts. This is supported by the redshift evolution in EW(H$α$) profiles, where there is rapid increase in EW(H$α$) with radius within the half-light radius at $z=5.3$ but only significantly increasing EW(H$α$) with radius in the outer disk at $z=0.5$.

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arXiv2024

FRESCO: The Paschen-$α$ Star Forming Sequence at Cosmic Noon

We present results from the JWST First Reionization Epoch Spectroscopically Complete Observations survey (FRESCO) on the star forming sequence of galaxies at $1.0 9.5 M_\odot$ that are lower than found in many earlier studies by up to 0.6 dex, but in good agreement with recent results obtained with the Prospector fitting framework. The difference log(SFR(Pa$α$)-SFR(Prospector)) is -0.09 $\pm$ 0.04 dex at $10^{10-11} M_\odot$. We also measure the empirical relation between Paschen-$α$ luminosity and rest-frame H band magnitude and find that the scatter is only 0.04 dex lower than that of the SFR-M* relation and is much lower than the systematic differences among relations in the literature due to various methods of converting observed measurements to physical properties. We additionally identify examples of sources -- that, with standard cutoffs via the UVJ diagram, would be deemed quiescent -- with significant, typically extended, Paschen-$α$ emission. Our results may be indicative of the potential unification of methods used to derive the star forming sequence with careful selection of star forming galaxies and independent star formation rate and stellar mass indicators.

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arXiv2024

5-25 $μ$m Galaxy Number Counts from Deep JWST Data

Galaxy number counts probe the evolution of galaxies over cosmic time, and serve as a valuable comparison point to theoretical models of galaxy formation. We present new galaxy number counts in eight photometric bands between 5 and 25 $μ$m from the Systematic Mid-infrared Instrument Legacy Extragalactic Survey (SMILES) and the JWST Advanced Deep Extragalactic Survey (JADES) deep MIRI parallel, extending to unprecedented depth. By combining our new MIRI counts with existing data from Spitzer and AKARI, we achieve counts across 3-5 orders of magnitude in flux in all MIRI bands. Our counts diverge from predictions from recent semi-analytical models of galaxy formation, likely owing to their treatment of mid-infrared aromatic features. Finally, we integrate our combined JWST-Spitzer counts at 8 and 24 $μ$m to measure the cosmic infrared background (CIB) light at these wavelengths; our measured CIB fluxes are consistent with those from previous mid-infrared surveys, but larger than predicted by some models based on TeV blazar data.

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