Spectral Energy Distribution Fitting Analysis Research Articles

Deficit of Hot Dust in Low-redshift Active Galactic Nuclei

We assemble a broadband spectral energy distribution (SED) ranging from the optical to the mid-infrared of nearby active galactic nuclei (AGNs) at z < 0.4. The SED fitting analysis is performed using semiempirical templates derived from Palomar-Green quasars to classify the sample into normal, warm-dust-deficient (WDD), and hot-dust-deficient (HDD) AGNs. Kolmogorov–Smirnov tests reveal that HDD AGNs exhibit higher AGN luminosity on average than normal and WDD AGNs. The HDD fraction, on the other hand, is only weakly correlated with the black hole mass and inversely correlated with the Eddington ratio. By fixing the other parameters, we conclude that the HDD fraction is primarily connected with the AGN luminosity. This implies that there is a causal connection between the covering factor of the hot dust component and AGN luminosity, possibly due to the sublimation of the innermost dust or the thickening of the intervening gas in the broad-line region. Analysis of the outflow properties traced by the wing of [O iii]λ5007 suggests that outflows may be related to the formation and maintenance of the hot dust component. Finally, we demonstrate through comparison with previous studies that the classification of HDD AGNs requires careful subtraction of the host galaxy light.

A Candidate for the Least-massive Black Hole in the First 1.1 Billion Years of the Universe

We report a candidate of a low-luminosity active galactic nucleus (AGN) at z = 5 that was selected from the first near-infrared images of the JWST CEERS project. This source, named CEERS-AGN-z5-1 at absolute 1450 Å magnitude M 1450 = −19.5 ± 0.3, was found via a visual selection of compact sources from a catalog of Lyman break galaxies at z > 4, taking advantage of the superb spatial resolution of the JWST/NIRCam images. The 20 photometric data available from CFHT, Hubble Space Telescope, Spitzer, and JWST suggest that the continuum shape of this source is reminiscent of that for an unobscured AGN, and there is a clear color excess in the filters where the redshifted Hβ+[O iii] and Hα are covered. The estimated line luminosity is L Hβ+[O III] = 1043.0 erg s−1 and L Hα = 1042.9 erg s−1 with the corresponding rest-frame equivalent width EWHβ+[O III] = 1100 Å and EWHα = 1600 Å, respectively. Our spectral energy distribution fitting analysis favors the scenario that this object is either a strong broad-line emitter or even a super-Eddington accreting black hole (BH), although a possibility of an extremely young galaxy with moderate dust attenuation is not completely ruled out. The bolometric luminosity, L bol = 2.5 ± 0.3 × 1044 erg s−1, is consistent with those of z < 0.35 broad-line AGNs with M BH ∼ 106 M ⊙ accreting at the Eddington limit. This new AGN population in the first 1.1 billion years of the universe may close the gap between the observed BH mass range at high redshift and that of BH seeds. Spectroscopic confirmation is awaited to secure the redshift and its AGN nature.

Fitting spectral energy distributions of FMOS-COSMOS emission-line galaxies atz∼ 1.6: Star formation rates, dust attenuation, and [OIII]λ5007 emission-line luminosities

We perform a spectral energy distribution fitting analysis on a COSMOS photometric sample covering the ultra-violet up to the far-infrared wavelengths and including emission lines from the Fiber Multi-Object Spectrograph survey. The sample consists of 182 objects with Hαand [OIII]λ5007 emission line measurements lying in a redshift range of 1.40 &lt; z &lt; 1.68. We obtain robust estimates of the stellar mass and star-formation rate spanning over a range of 109.5 − 1011.5M⊙and 101 − 103M⊙yr−1from the Bayesian analysis performed with CIGALE and using continuum photometry and Hαfluxes. Combining photometry and spectroscopy gives secure estimations of the amount of dust attenuation for both continuum and line emissions. We obtain a median attenuation ofAHα = 1.16 ± 0.19 mag andA[OIII] = 1.41 ± 0.22 mag. Hαand [OIII]λ5007 attenuations are found to increase with stellar mass, confirming previous findings with Hα. A difference of 57% in the attenuation experienced by emission lines and continuum is found to be in agreement with the emission lines being more attenuated than the continuum emission. Implementation of new CLOUDY HII-region models in CIGALE enables good fits of the Hα, Hβ, [OIII]λ5007 emission lines with discrepancies smaller than 0.2 dex in the predicted fluxes. Fitting the [NII]λ6584 line is found challenging due to well-known discrepancies in the locus of galaxies in the [NII]-BPT diagram at intermediate and high redshifts. We find a positive correlation between SFR andL[OIII]λ5007 after correcting for dust attenuation and we derive the linear relation log10(SFR/M⊙yr−1)=log10(L[OIII]/ergs s−1)−(41.20 ± 0.02). Leaving the slope as a free parameter leads to log10(SFR/M⊙yr−1)=(0.83 ± 0.06)log10(L[OIII]/ergs s−1)−(34.01 ± 2.63). The spread in the relation is driven by differences in the gas-phase metallicity and ionization parameter accounting for a 0.24 dex and 1.1 dex of the dispersion, respectively. We report an average value of logU ≈ −2.85 for this sample of galaxies. Including HII-region models to fit simultaneously photometric data and emission line fluxes is paramount to analyses of upcoming data sets from large spectroscopic surveys of the future, such as MOONS and PFS.

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

We study the IB(s)m galaxy IC 3476 observed in the context of the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE), a blind narrow-band Hα+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT. The deep narrow-band image reveals a very pertubed ionised gas distribution that is characterised by a prominent banana-shaped structure in the front of the galaxy formed of giant HII regions crossing the stellar disc. Star-forming structures, at ∼8 kpc from the edges of the stellar disc, are also detected in a deep far-ultraviolet ASTROSAT/UVIT image. This particular morphology indicates that the galaxy is undergoing an almost edge-on ram pressure stripping event. The same Hα+[NII] image also shows that the star formation activity is totally quenched in the leading edge of the disc, where the gas has been removed during the interaction with the surrounding medium. The spectral energy distribution fitting analysis of the multi-frequency data indicates that this quenching episode is very recent (∼50 Myr), and roughly corresponds to an increase of the star formation activity by a factor of ∼161% in the inner regions with respect to that expected for secular evolution. The analysis of these data, whose angular resolution enables the study of the induced effects of the perturbation down to the scale of individual HII regions (req ≃ 40 pc), also suggests that the increase of star formation activity is due to the compression of the gas along the stellar disc of the galaxy, which is able to increase its mean electron density and boost the star formation process producing bright HII regions with luminosities up to L(Hα) ≃ 1038 erg s−1. The combined analysis of the VESTIGE data with deep IFU spectroscopy gathered with MUSE and with high spectral resolution Fabry Perot data also indicates that the hydrodynamic interaction has deeply perturbed the velocity field of the ionised gas component while leaving that of the stellar disc unaffected. The comparison of the data with tuned high-resolution hydrodynamic simulations accounting for the different gas phases (atomic, molecular, ionised) consistently indicates that the perturbing event is very recent (50–150 Myr), once again confirming that ram pressure stripping is a violent phenomenon that is able to perturb the evolution of galaxies in rich environments on short timescales.

Discovery of a Nearby Young Brown Dwarf Disk

Abstract We report the discovery of the youngest brown dwarf with a disk at 102 pc from the Sun, WISEA J120037.79−784508.3 (W1200−7845), via the Disk Detective citizen science project. We establish that W1200−7845 is located in the Myr old ε Cha association. Its spectral energy distribution (SED) exhibits clear evidence of an infrared (IR) excess, indicative of the presence of a warm circumstellar disk. Modeling this warm disk, we find the data are best fit using a power-law description with a slope α = −0.94, which suggests that it is a young, Class II type disk. Using a single blackbody disk fit, we find and . The near-IR spectrum of W1200−7845 matches a spectral type of M6.0 0.5, which corresponds to a low surface gravity object, and lacks distinctive signatures of strong Paβ or Brγ accretion. Both our SED fitting and spectral analysis indicate that the source is cool (T eff = 2784–2850 K), with a mass of 42–58 M Jup, well within the brown dwarf regime. The proximity of this young brown dwarf disk makes the system an ideal benchmark for investigating the formation and early evolution of brown dwarfs.

A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). III. Discovery of a z = 4.72 Radio Galaxy with the Lyman Break Technique

Abstract We report a discovery of a z = 4.72 radio galaxy, HSC J083913.17+011308.1, using the Lyman break technique with the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) catalog for Very Large Array Faint Images of the Radio Sky at Twenty centimeter radio sources. The number of known high-z radio galaxies (HzRGs) at z &gt; 3 is quite small to constrain the evolution of HzRGs so far. The deep and wide-area optical survey by HSC-SSP enables us to apply the Lyman break technique to a large search for HzRGs. For an HzRG candidate among pre-selected r-band dropouts with a radio detection, a follow-up optical spectroscopy with the Gemini Multi-Object Spectrographs (GMOS)/Gemini has been performed. The obtained spectrum presents a clear Lyα emission line redshifted to z = 4.72. The spectral energy distribution fitting analysis with the rest-frame UV and optical photometries suggests the massive nature of this HzRG with . The small equivalent width of Lyα and the moderately red UV colors indicate its dusty host galaxy, implying a chemically evolved and dusty system. The radio spectral index does not meet a criterion for an ultra-steep spectrum, of −1.1 and of −0.9, demonstrating that the HSC-SSP survey compensates for a subpopulation of HzRGs that are missed in surveys focusing on an ultra-steep spectral index.

Timing the earliest quenching events with a robust sample of massive quiescent galaxies at 2 &amp;lt; z &amp;lt; 5

ABSTRACT We present a sample of 151 massive (M* &amp;gt; 1010 M⊙) quiescent galaxies at 2 &amp;lt; z &amp;lt; 5, based on a sophisticated Bayesian spectral energy distribution fitting analysis of the CANDELS UDS and GOODS-South fields. Our sample includes a robust sub-sample of 61 objects for which we confidently exclude low-redshift and star-forming solutions. We identify 10 robust objects at z &amp;gt; 3, of which 2 are at z &amp;gt; 4. We report formation redshifts, demonstrating that the oldest objects formed at z &amp;gt; 6; however, individual ages from our photometric data have significant uncertainties, typically ∼0.5 Gyr. We demonstrate that the UVJ colours of the quiescent population evolve with redshift at z &amp;gt; 3, becoming bluer and more similar to post-starburst galaxies at lower redshift. Based upon this, we construct a model for the time evolution of quiescent galaxy UVJ colours, concluding that the oldest objects are consistent with forming the bulk of their stellar mass at z ∼ 6–7 and quenching at z ∼ 5. We report spectroscopic redshifts for two of our objects at z = 3.440 and 3.396, which exhibit extremely weak Ly α emission in ultra-deep VANDELS spectra. We calculate star formation rates based on these line fluxes, finding that these galaxies are consistent with our quiescent selection criteria, provided their Ly α escape fractions are &amp;gt;3 and &amp;gt;10 per cent, respectively. We finally report that our highest redshift robust object exhibits a continuum break at λ ∼ 7000 Å in a spectrum from VUDS, consistent with our photometric redshift of $z_\mathrm{phot}=4.72^{+0.06}_{-0.04}$. If confirmed as quiescent, this object would be the highest redshift known quiescent galaxy. To obtain stronger constraints on the times of the earliest quenching events, high-SNR spectroscopy must be extended to z ≳ 3 quiescent objects.

Massive and old quiescent galaxies at high redshift

Aims. Questions of how massive quiescent galaxies rapidly assembled and how abundant they are at high redshift are increasingly important in the study of galaxy formation. Looking at these systems can shed light on the processes of galaxy mass assembly and quenching of the star formation at early epochs. In order to address these questions, we aim to identify and characterize massive quiescent galaxies from z ∼ 2.5 out to the highest redshifts at which these systems can be found. The final purpose is to compare the results with the predictions of state-of-the-art semi-analytical models of galaxy formation and evolution. Methods. We defined observer-frame color–color diagrams to optimally select quiescent galaxies at z &gt; 2.5 and applied them to the COSMOS2015 catalog. We refined the spectral energy distribution (SED) fitting analysis for the selected candidates to confirm their quiescent nature, then derived their number density, mass density, and stellar mass functions. Finally, we compared the results with previous observations and some current semi-analytic models. Results. We selected candidates for quiescent galaxies in the redshift range 2.5 ≲ z ≲ 4.5 from the COSMOS2015 catalog by means of two color–color diagrams. The additional SED fitting analysis allowed us to select 128 galaxies, consistent with being massive (log(M*/M⊙)≥10.6), old (ages ≳0.5 Gyr), and quiescent (log(sSFR [yr−1]) ≤ −10.5) objects at high redshift (2.5 &lt; z &lt; 4.5). Their number and mass densities are in fair agreement with previous observations and, if confirmed, show a discrepancy with current semi-analytical models of galaxy formation and evolution, that underpredict the number of massive quiescent systems up to a factor of ∼12 at 2.5 ≤ z &lt; 3.0 and ∼10 at z ∼ 4.0. The evolution of the stellar mass functions (SMFs) of these systems is similar to previous estimates and indicates a disagreement with models, particularly with regard to the shape of the SMF. Conclusions. The present results add further evidence to the possibility that massive and quiescent galaxies can exist out to at least z ∼ 4. If future spectroscopic observations carried out with, for example, the James Webb Space Telecope (JWST), confirm the substantial presence of such a population, further work on modeling the stellar mass assembly, as well as supermassive black hole accretion and feedback processes at early cosmic epochs, is needed to understand how these systems formed, evolved, and quenched their star formation.

The UV spectral slope β and stellar population of most active star-forming galaxies at z ∼ 4

Abstract We investigate a stellar population of star-forming galaxies at z ∼ 4 by focusing on the slope of their rest-frame ultraviolet (UV) continuum, β, where fλ ∝ λβ. We investigate a sample of bright Lyman break galaxies (LBGs) with i′ ≤ 26.0 in the Subaru/XMM-Newton Deep Survey field by using a spectral energy distribution fitting analysis. We find that the apparently redder (βobs &amp;gt; −1.73) LBGs tend to be dusty (AV &amp;gt; 1.0), and have young stellar populations (βint &amp;lt; −2.42) and intrinsically active star-forming galaxies (SFR ≳ a few $\times \ 10^{2}\, {M_{\odot }}\:\mbox{yr}^{-1}$). This means that a significant fraction of the UV-selected LBGs at z ∼ 4 contains on-going, active, and dust-obscured star-forming galaxies. We compare the infrared to UV luminosity ratio, which is estimated from our optical/near-infrared data assuming dust attenuation laws, with sub-millimeter observations from previous works. The result suggests that the Calzetti-like dust attenuation law is preferable for active and dusty star-forming LBGs at z = 4. We also find that an extrapolation of the βint–MUV, int relation toward the fainter magnitude range below our sample magnitude limit intersects the βobs–MUV, obs relation previously obtained in deeper narrow-area observations at MUV = −18.9 and β = −1.94, which coincides with the break point of the βobs–MUV, obs relation observed so far. This coincidence suggests that we see an almost dust-free population at MUV, obs ≳ −18.9.

Stellar contents and star formation in the NGC 7538 region

Deep optical photometric data on the NGC 7538 region were collected and combined with archival data sets from $Chandra$, 2MASS and {\it Spitzer} surveys in order to generate a new catalog of young stellar objects (YSOs) including those not showing IR excess emission. This new catalog is complete down to 0.8 M$_\odot$. The nature of the YSOs associated with the NGC 7538 region and their spatial distribution are used to study the star formation process and the resultant mass function (MF) in the region. Out of the 419 YSOs, $\sim$91\% have ages between 0.1 to 2.5 Myr and $\sim$86\% have masses between 0.5 to 3.5 M$_\odot$, as derived by spectral energy distribution fitting analysis. Around 24\%, 62\% and 2\% of these YSOs are classified to be the Class I, Class II and Class III sources, respectively. The X-ray activity in the Class I, Class II and Class III objects is not significantly different from each other. This result implies that the enhanced X-ray surface flux due to the increase in the rotation rate may be compensated by the decrease in the stellar surface area during the pre-main sequence evolution. Our analysis shows that the O3V type high mass star `IRS 6' might have triggered the formation of young low mass stars up to a radial distance of 3 pc. The MF shows a turn-off at around 1.5 M$_\odot$ and the value of its slope `$\Gamma$' in the mass range $1.5 <$M/M$_\odot < 6$ comes out to be $-1.76\pm0.24$, which is steeper than the Salpeter value.