arXiv subjects

Tanio Díaz Santos

Publications and source records attributed to Tanio Díaz Santos.

9 recordsLinked to original sources

arXiv2026

ALMA2040: Mapping the Spatially Resolved Dust and Star Formation Physics Driving High-z Galaxy Assembly

Interstellar dust reprocesses approximately half of the starlight emitted across cosmic history. However, dust temperature, which is essential to convert continuum flux into dust mass, molecular gas mass, and obscured star-formation rates, remains largely unconstrained on sub-galactic scales at high redshift. While single-band ALMA imaging has characterized continuum sizes for hundreds of z>1 galaxies, single-frequency measurements cannot separate the dust mass column from the local dust heating. To date, spatially resolved (<0.5-arcsec) multi-band dust temperatures exist in the literature for only ~10 extreme systems (quasars, hyperluminous starbursts, or strongly lensed galaxies) at z>1, with ongoing programs within a few years adding at most a few dozen submillimeter or UV-bright galaxies. This still leaves typical main-sequence disks largely unexplored across cosmic history. With an anticipated ~30 times improvement in continuum sensitivity (compared to the current ALMA), simultaneous multi-band receivers, and (sub-)kpc angular resolution, ALMA2040 will transform resolved dust thermometry into a systematic survey science. Here, we present the scientific rationale and technical requirements, highlighting a future statistically meaningful survey with > 100 representative main-sequence galaxies across cosmic epochs. Realistic visibility simulations demonstrate that ALMA2040 measures radial temperature gradients with ~0.5-4 K precision (L_IR~10^{12} L_sun in 2 h on-source at z~2). These measurements will break the degeneracy between intrinsic compactness and temperature gradients, deliver the first extinction-free, temperature-calibrated resolved star-formation relations, and uniquely trace radiative feedback and disk maturation from cosmic noon to cosmic dawn.

astro-ph.IM↗

arXiv2026

Breaking the Blend: A multi-tracer kinematic decomposition method for IFS data applied to disentangling the AGN outflow and circumnuclear ring in NGC 5728 with JWST

Integral field spectroscopy (IFS) of the central kiloparsecs of active galactic nuclei (AGN) reveals a mixture of spatially coincident emission from star-formation and AGN feedback exciting the interstellar medium. Disentangling these components remains a challenge, as most spectral tracers are affected by both processes, limiting robust interpretation of kinematics and energetics. We present a new framework for decomposing IFS data into distinct components on a spaxel-by-spaxel basis using a multi-tracer, stacked kinematics approach. This method combines kinematic modelling with imposed flux decomposition per spaxel, quantifying the contribution of each component across the field of view. We apply this method to JWST IFS observations of the Seyfert galaxy NGC 5728 from the Galaxy Activity, Torus, and Outflow Survey (GATOS), analysing twelve mid-infrared fine-structure lines (4.49 < $λ$ < 25.89 $μ$m, 7.9 < IP < 126.2 eV). We find that the circumnuclear emission can be decomposed into two dominant components: a star-forming ring and an AGN-driven biconical outflow. Our method separates these structures and recovers their detailed spatial morphology. This framework provides a general and scalable method for physically motivated component separation in IFS data, applicable across many wavelength ranges and targets, enabling reliable interpretation of complex emission line structures (or morphologies) in active galaxies and beyond.

astro-ph.GA↗

arXiv2026

PAHSPECS: JWST/MIRI Spectroscopy of PAHs at Cosmic Noon

The physical conditions of the interstellar medium (ISM) are thought to differ greatly at high redshifts compared to local galaxies. Polycyclic aromatic hydrocarbons (PAHs) are key ISM constituents, mediating the heating and cooling of gas in photo-dissociation regions. However, PAHs are unexplored in main-sequence (MS) galaxies at z~1-2 (cosmic noon), limiting our view of the ISM's thermal and chemical balance. We present the PAH Spectroscopic Survey (PAHSPECS) JWST program, the first MIRI/MRS survey of the 3.3, 6.2, 7.7, 8.6 and 11.3$μ$m PAH features in MS galaxies at z~1. The five targets come from the deep ALMA CO and continuum flux-limited sample in the HUDF. We detect the 6.2, 7.7 and 11.3$μ$m PAHs in all galaxies, and the 3.3$μ$m feature in only two. Spectral energy distribution (SED) fitting to broad-band mid-IR photometry recovers the 6.2 and 7.7$μ$m PAH luminosities derived from spectral decomposition of the MRS spectra to within ~25% accuracy. However, the 3.3 and 11.3$μ$m features are overestimated by ~50% (up to 3-5x). Spatially resolved maps of ASPECS-6, the most extended source, show variations of the 7.7$μ$m PAH contribution to the MIRI F1500W flux, suggesting that while photometry can infer PAH luminosity accurately, IFU spectroscopy is necessary to study variations in PAH ratios and characterize galaxy dust properties. The PAH fraction of the total dust mass from photometric SED modeling roughly agrees with the $L_{\rm PAH}/L_{\rm IR}$ ratio measured from spectroscopy, but the correlation is not as tight as models predict. On average, PAHSPECS galaxies show an excess in 6.2$μ$m equivalent width relative to nearby dusty luminous systems, but lower 3.3$μ$m equivalent widths than local systems, similar to higher-mass starbursts at z~1-3. This points to differential changes in the size distributions of neutral and ionized PAHs in cosmic noon galaxies.

astro-ph.GA↗

arXiv2026

PAHSPECS: Polycyclic aromatic hydrocarbon properties at cosmic noon with JWST/MIRI MRS

Context. Cosmic noon (z ~ 1-3) marks the peak of the cosmic star-formation rate density, when dust-obscured star formation dominated galaxy growth. Mid-infrared spectroscopy probes the interstellar medium through PAH emission, whose band ratios trace PAH charge, size, and local radiation-field conditions. Aims. We characterize the PAH properties of five z ~ 1.1 star-forming galaxies from the PAHSPECS survey and investigate how their PAH luminosities and band ratios relate to global galaxy properties. We compare them with local luminous infrared galaxies (LIRGs) to assess whether PAH emission at cosmic noon differs from that nearby. Methods. We analyze JWST/MIRI MRS observations of five ASPECS galaxies in the HUDF. Integrated spectra are extracted with wavelength-dependent apertures and modeled with CAFE, including ancillary photometry to constrain the dust emission. Stellar masses and SFRs are derived with Prospector. Results. Compared to local LIRGs, most PAHSPECS sources show higher 6.2/7.7 and lower 11.3/7.7 ratios, suggesting an ionized PAH component weighted toward smaller grains. The 3.3/11.3 ratio is less constrained, since the 3.3 micron feature is detected in only two sources. Within the sample, 11.3/7.7 increases with sSFR and star-formation surface density, while 6.2/7.7 decreases with sSFR, consistent with preferential processing of small ionized PAH carriers. ASPECS-15, the AGN-hosting source, has the lowest 6.2/7.7 ratio and highest sSFR, suggesting a reduced contribution from small PAHs, potentially due to AGN activity. The 7.7 micron luminosity follows the local L7.7-SFR relation, supporting its use as a star-formation tracer at z ~ 1. Conclusions. PAH emission at cosmic noon appears shaped by different ISM conditions than in nearby starburst galaxies, likely reflecting more intense radiation fields, while the 7.7 micron feature remains a robust SFR tracer.

astro-ph.GA↗

arXiv2026

GATOS XI : Excess dust heating in the Narrow Line Regions of nearby AGN revealed with JWST/MIRI

We present JWST/MIRI imaging of eight nearby Active Galactic Nuclei (AGN) from the GATOS survey to investigate the physical conditions of extended dust in their narrow line regions (NLRs). In four galaxies (ESO 428-G14, NGC 4388, NGC 3081, and NGC 5728), we detect spatially resolved dust structures extending ~100-200 pc along the NLR. In these systems, we find a strong link between the morphology of the dust, the radio ejecta, and the coronal [Si VI] emission, implying that dust carries imprints of the processes shaping the NLR. Using spatially resolved spectral energy distributions, we show that dust in the NLR has systematically steeper slopes than star forming clumps. This dust emits at temperatures in the range 150 - 220 K, at a distance of ~150 pc from the nucleus. Using simple models, we show that, even under optimistic assumptions of grain size and AGN luminosity, the excess MIR emission cannot be explained by AGN illumination alone. We interpret this excess heating as in-situ. We show that shocks with velocities of $v_{\rm shock} \sim 200- 400 \, \rm km/s$ in dense gas can close this gap, and in some cases even account for the total observed emission. This, combined with multiple lines of evidence for shocks in these regions, supports a scenario in which shocks not only coexist with dust but may be playing a key role in heating it. Our findings reveal shocks may be an important and previously overlooked driver of extended dust emission in the central hundreds of parsecs in AGN.

astro-ph.GA↗

arXiv2025

Spatially resolved dust properties over 50 kpc in a hyperluminous galaxy merger at $z = 4.6$

We present spatially resolved dust-continuum ALMA observations from rest-frame $\sim$60 to $\sim$600 $μ$m (bands 3-10) of the hyperluminous hot dust-obscured galaxy (hot DOG) WISE J224607.6-052634.9 (W2246-0526), at redshift $z=4.6$. W2246-0526 is interacting with at least three companion galaxies, forming a system connected by tidal streams. We model the multiwavelength ALMA observations of the dust continuum using a modified blackbody, from which we derive the dust properties (mass, emissivity index, area of the emitting region, and temperature) in the hot DOG and resolved structures across a region of nearly $\sim$50 kpc. The peak temperature at the location of the hot DOG, $\sim$110 K, is likely the consequence of heating by the central quasar. The dust temperature drops to $\sim$40 K at a radius of $\sim$8 kpc, suggesting that heating by the quasar beyond that distance is nondominant. The dust in the connecting streams between the host and companion galaxies is at temperatures between 30-40 K, typical of starburst galaxies, suggesting it is most likely heated by recent, in-situ star formation. This is the first time dust properties are spatially resolved over several tens of kpc in a galaxy system beyond Cosmic Noon --this is more than six times the scales previously probed in galaxies at those redshifts.

astro-ph.GA↗

arXiv2024

A benchmark for extreme conditions of the multiphase interstellar medium in the most luminous hot dust-obscured galaxy at z = 4.6

WISE J224607.6-052634.9 (W2246-0526) is a hot dust-obscured galaxy at $z$ = 4.601, and the most luminous obscured quasar known to date. W2246-0526 harbors a heavily obscured supermassive black hole that is most likely accreting above the Eddington limit. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in seven bands, including band 10, of the brightest far-infrared (FIR) fine-structure emission lines of this galaxy: [OI]$_{63μm}$, [OIII]$_{88μm}$, [NII]$_{122μm}$, [OI]$_{145μm}$, [CII]$_{158μm}$, [NII]$_{205μm}$, [CI]$_{370μm}$, and [CI]$_{609μm}$. A comparison of the data to a large grid of Cloudy radiative transfer models reveals that a high hydrogen density ($n_{H}\sim3\times10^3$ cm$^{-3}$) and extinction ($A_{V}\sim300$ mag), together with extreme ionization ($log(U)=-0.5$) and a high X-ray to UV ratio ($α_{ox}\geq-0.8$) are required to reproduce the observed nuclear line ratios. The values of $α_{ox}$ and $U$ are among the largest found in the literature and imply the existence of an X-ray-dominated region (XDR). In fact, this component explains the a priori very surprising non-detection of the [OIII]$_{88μm}$ emission line, which is actually suppressed, instead of boosted, in XDR environments. Interestingly, the best-fitted model implies higher X-ray emission and lower CO content than what is detected observationally, suggesting the presence of a molecular gas component that should be further obscuring the X-ray emission over larger spatial scales than the central region that is being modeled. These results highlight the need for multiline infrared observations to characterize the multiphase gas in high redshift quasars and, in particular, W2246-0526 serves as an extreme benchmark for comparisons of interstellar medium conditions with other quasar populations at cosmic noon and beyond.

astro-ph.GA↗

arXiv2022

Low frequency radio continuum imaging and SED modeling of 11 LIRGs: radio-only and FUV to radio bands

We present the detailed analysis of 11 local luminous infrared galaxies (LIRGs) from ultraviolet through far-infrared to radio ($\sim$70 MHz to $\sim$15 GHz) bands. We derive the astrophysical properties through spectral energy distribution (SED) modeling using the Code Investigating GALaxy Emission (CIGALE) and UltraNest codes. The radio SEDs include our new observations at 325 and 610 MHz from the GMRT and the measurements from public archives. Our main results are (1) radio SEDs show turnovers and bends, (2) the synchrotron spectral index of the fitted radio spectra ranges between $-$0.5 and $-$1.7, and (3) the infrared luminosity, dust mass, dust temperature, stellar mass, star-formation rates (SFRs) and AGN fraction obtained from CIGALE falls in the range exhibited by galaxies of the same class. The ratio of 60$μ$m infrared and 1.4 GHz radio luminosity, the 1.4 GHz thermal fraction, and emission measure range between 2.1 and 2.9, 0.1% and 10%, 0.02 and 269.5$\times$10$^{6}$ cm$^{-6}$ pc, respectively. We conclude that the turnovers seen in the radio SEDs are due to free-free absorption; this is supported by the low AGN fraction derived from the CIGALE analysis. The decomposed 1.4 GHz thermal and nonthermal radio luminosities allowed us to compute the star formation rate (SFR) using scaling relations. A positive correlation is observed between the SFR$_{IR}$ obtained 10 Myr ago (compared to 100 Myr ago) and 1.4 GHz radio (total and nonthermal) because similar synchrotron lifetimes are expected for typical magnetic field strengths observed in these galaxies ($\approx$50$μ$G).

astro-ph.GA↗

arXiv2015

Resolving the AGN and host emission in the mid-infrared using a model-independent spectral decomposition

We present results on the spectral decomposition of 118 Spitzer Infrared Spectrograph (IRS) spectra from local active galactic nuclei (AGN) using a large set of Spitzer/IRS spectra as templates. The templates are themselves IRS spectra from extreme cases where a single physical component (stellar, interstellar, or AGN) completely dominates the integrated mid-infrared emission. We show that a linear combination of one template for each physical component reproduces the observed IRS spectra of AGN hosts with unprecedented fidelity for a template fitting method, with no need to model extinction separately. We use full probability distribution functions to estimate expectation values and uncertainties for observables, and find that the decomposition results are robust against degeneracies. Furthermore, we compare the AGN spectra derived from the spectral decomposition with sub-arcsecond resolution nuclear photometry and spectroscopy from ground-based observations. We find that the AGN component derived from the decomposition closely matches the nuclear spectrum, with a 1-sigma dispersion of 0.12 dex in luminosity and typical uncertainties of ~0.19 in the spectral index and ~0.1 in the silicate strength. We conclude that the emission from the host galaxy can be reliably removed from the IRS spectra of AGN. This allows for unbiased studies of the AGN emission in intermediate and high redshift galaxies -currently inaccesible to ground-based observations- with archival Spitzer/IRS data and in the future with the Mid-InfraRed Instrument of the James Webb Space Telescope. The decomposition code and templates are available at http://www.denebola.org/ahc/deblendIRS.

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