arXiv subjects

C. Bracci

Publications and source records attributed to C. Bracci.

8 recordsLinked to original sources

arXiv2026

Fast, dust-poor outflows in the local candidate dual AGN MCG-03-34-64 observed with VLT/ERIS

We present VLT/ERIS IFU J-band observations of MCG-03-34-64, a nearby (z = 0.0167) Seyfert galaxy hosting a candidate dual AGN system with a separation of ~100 pc between the nuclei. The observations cover, among others, the HeI1.083um, [FeII]1.257um and Pa$\beta$ emission lines, over a FoV of 3"x3"(~1x1 kpc$^2$). We analyse the ionised gas kinematics and identify two regions with enhanced velocity dispersion (W80~1500 km/s), suggestive of fast outflowing gas, spatially coincident with the position of the two candidate active nuclei. The spectra of the two outflows show a prominent blueshifted wing with velocities vmax ~ -1700 km/s corresponding to the highest 2-5 percentiles of samples of local AGN with similar bolometric luminosities. For the ionised phase of the two outflows, we derive comparable masses of $(4\pm1)\times 10^5$ $M_{\odot}$ and mass outflow rates of $20\pm5$ $M_{\odot}$/yr. The two distinct outflows could be associated with the two nuclei, or be generated by the interaction of the radio jet with the ISM. We also analyse the peculiar profile of the [Fe VII]6087A optical coronal line from an archival VLT/X-shooter spectrum. The comparison with the [NeV]3425A and [FeII]1.257um profiles indicates that [Fe VII] emission likely arises only from the outflow. The absence of the systemic component in [Fe VII] - unlike in [NeV], which has similar ionisation potential and critical density - suggests suppression of [Fe VII] due to iron depletion onto dust grains, while its detection in the outflow implies a lower dust content than in the host ISM. The additional information gained from the ERIS data are consistent with the scenario of a dual AGN, however further observations are required to confirm its nature.

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arXiv2025

Cosmic Duets I. High-spatial resolution spectroscopy of dual and lensed AGN with MUSE-NFM

We present the first-year results of the MUSE Large Program "Cosmic Duets", whose goal is to obtain adaptive-optics assisted MUSE observations with an angular resolution of 0.1"-0.2" in order to provide integral-field spectroscopy of sub-arcsec separation dual and lensed active galactic nucleus (AGN) candidates. These observations reveal previously unexplored properties of dual and lensed systems that are key to understanding galaxy evolution, supermassive black hole mergers, and strong-lensing modeling. Targets were efficiently selected using the Gaia multipeak (GMP) technique, which identifies pairs of point-like sources with separations below 0.8" in the Gaia catalog. MUSE spatially resolved spectroscopy provides accurate redshifts, ionization diagnostics, and identification of absorption systems along the line of sight. We report results for 30 GMP targets at z=0.5-3.5. All systems show at least 2 spatially resolved components. 19 objects are confirmed as AGN multiplets, including 6 dual AGN, 10 doubly lensed quasars, and 3 quadruply lensed systems, while the remaining 11 correspond to chance alignments with foreground stars. Among all the spectroscopically confirmed dual AGN in the literature, 27 pairs have projected separations below 7kpc in this redshift regime, and our sample accounts for 22% of the total. We studied dual and lensed AGN distributions as a function of redshift, magnitude, and projected separation while accounting for selection effects, and we find that bright systems are dominated by lensed quasars, whereas the relative fraction of dual AGN increases at fainter magnitudes. This first-year sample demonstrates the high efficiency of GMP selection combined with MUSE spectroscopy for identifying sub-arcsec dual and lensed AGN. The full program, targeting 150 systems, will enable statistical studies of dual AGN and constraints on mass distribution in lensing galaxies.

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arXiv2025

MIRACLE III. JWST/MIRI expose the hidden role of the AGN outflow in NGC 1068

We present new JWST IFS observations of the active galaxy NGC 1068, combining Mid-IR and optical IFS data from MIRI and MUSE to characterize the multi-phase circumnuclear gas properties and its interaction with the AGN outflow and radio jet. MIRI data trace the multiphase gas emission up to 400 pc from the nucleus at 20--60 pc resolution, unveiling a clumpy ionized structure around the radio hot-spots and a rotating warm molecular disc. Innovative Mid-IR diagnostic diagrams highlight the role of the AGN as the main excitation source for the ionized gas in the entire MIRI field of view, consistent with optical diagnostics, and supporting the AGN-driven wind scenario. Density sensitive [NeV] and [ArV] Mid-IR transitions reveal high-density clumps (n_e > 10**4 cm**-3) along the edges of the jet and outflow, tracing gas compression by the expanding wind. We combined multi-cloud kinematic (MOKA) and photo-ionization (HOMERUN) modeling to characterize the ionized outflow properties and found that [OIV] traces an outflow 300 km/s faster than that inferred from [OIII], showing that the two lines originate from distinct gas components. This kinematic dichotomy is confirmed by the photoionization analysis, which requires a dust-poor component dominating the optical lines and a dust-rich component responsible for the Mid-IR emission. The Mid-IR-revealed dusty component carries a significantly larger ionized-gas mass than what can be inferred from optical lines alone, showing that most of the outflowing mass is hidden from classical optical diagnostics. Our modelling point to a two-stage acceleration scenario, with velocities up to ~2000 km/s, consistent with an energy-driven wind. Our findings indicates that the outflow entrains up to a few 10**6 solar masses of ionized gas and couples efficiently with the surrounding ISM, injecting turbulence and impacting the host-galaxy environment.

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arXiv2025

Tracing nitrogen enrichment across cosmic time with JWST

We present a comprehensive analysis of the nitrogen-to-oxygen (N/O) abundance ratio in a sample of ~ 660 star-forming galaxies at redshift z ~ 1-6, with a median redshift of z = 3.0, using deep JWST/NIRSpec spectroscopy. Leveraging detections of faint auroral emission lines in 92 galaxies at z>1 from both the MARTA survey and a large compilation of high-redshift literature objects, we derive direct electron temperature-based abundances for nitrogen and oxygen using rest-frame optical lines. We establish the first high-redshift calibrations of strong-line N/O diagnostics based on 'direct' abundance measurements, finding a mild evolution for the N2O2 = log([NII]6585/[OII]3727,3729) diagnostic and no clear evolution for the N2S2 = log([NII]6585/[SII]6717,6731) diagnostic compared to local realisations. We then investigate the N/O-O/H relation across cosmic time using both 'direct' abundances and strong-lines based measurements (additional 535 galaxies). We find evidence for mild but systematic nitrogen enhancement at high redshift: galaxies at z>1 exhibit N/O ratios elevated by ~0.18 dex (median offset) at fixed O/H compared to local trends, with a more pronounced enhancement at low metallicity (i.e. 12 + log(O/H) < 8.1), where the offset reaches up to ~0.4-0.5 dex. We consider several scenarios to explain the observed trends, including bursty star formation, differential metal loading, and inflows of pristine gas. Our results provide the most extensive confirmation of elevated N/O ratios at high-redshift to date based on rest-optical diagnostics and within a self-consistent frame.

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arXiv2025

M^3D: Mosaicking M33 with MUSE datacubes I. Unveiling the diversity of HII regions in M33 with MUSE

We present new VLT/MUSE observations of a 3 $\times$ 8 arcmin$^2$ mosaic along the southern major axis of the Local Group galaxy M33. These data provide an unprecedented view of the galaxy's interstellar medium (ISM) and allow us to resolve ionised nebulae at a spatial scale of $\approx$5 pc. We identified and catalogued 131 HII regions, down to H\alpha luminosities of $\approx 5\times$10$^{35}$ erg s$^{-1}$, one order of magnitude fainter than previous surveys on nearby galaxies beyond the Local Group, and we compared these regions with the spatial distribution of ionising stars and embedded star clusters. For each region, we extracted the corresponding integrated optical spectra and measured the intensity of key optical emission lines (H\beta, [OIII], [NII], H\alpha, [SII], [SIII]), other weaker optical lines when detectable, and Paschen lines to characterise the physical properties of the ioinised gas, such as density, dust attenuation, and metallicity. Our spatially resolved line ratio and flux maps reveal a remarkable diversity in ionisation properties, from dust-obscured regions hosting young stellar objects to highly ionised bubbles exhibiting high [OIII]/H\beta ratios. Our data reveal a diversity of ionisation fronts, ranging from well-defined to partial to absent. The radial profiles we obtained indicate the presence of both optically thin (density-bounded) HII regions permitting the escape of ionising photons and fully ionised, optically thick (ionisation-bounded) HII regions. The richness of this MUSE mosaic offers an unprecedented view of the ionised ISM at $\approx$5 pc resolution, providing direct insight into how stellar feedback shapes its environment.

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arXiv2025

Euclid: A machine-learning search for dual and lensed AGN at sub-arcsec separations

Cosmological models of hierarchical structure formation predict the existence of a widespread population of dual accreting supermassive black holes (SMBHs) on kpc-scale separations, corresponding to projected distances < 0".8 at redshifts higher than 0.5. However, close companions to known active galactic nuclei (AGN) or quasars (QSOs) can also be multiple images of the object itself, strongly lensed by a foreground galaxy, as well as foreground stars in a chance superposition. Thanks to its large sky coverage, sensitivity, and high spatial resolution, Euclid offers a unique opportunity to obtain a large, homogeneous sample of dual/lensed AGN candidates with sub-arcsec projected separations. Here we present a machine learning approach, in particular a Convolutional Neural Network (CNN), to identify close companions to known QSOs down to separations of $\sim\,$0".15 comparable to the Euclid VIS point spread function (PSF). We studied the effectiveness of the CNN in identifying dual AGN and demonstrated that it outperforms traditional techniques. Applying our CNN to a sample of $\sim\,$6000 QSOs from the Q1 Euclid data release, we find a fraction of about 0.25% dual AGN candidates with separation $\sim\,$0".4 (corresponding to $\sim$3 kpc at z=1). Estimating the foreground contamination from stellar objects, we find that most of the pair candidates with separation higher than 0".5 are likely contaminants, while below this limit, contamination is expected to be less than 20%. For objects at higher separation (>0".5, i.e. 4 kpc at z=1), we performed PSF subtraction and used colour-colour diagrams to constrain their nature. We present a first set of dual/lensed AGN candidates detected in the Q1 Euclid data, providing a starting point for the analysis of future data releases.

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arXiv2025

MIRACLE II: Unveiling the multi-phase gas interplay in the circumnuclear region of NGC 1365 via multi-cloud modeling

We present a multi-phase study of the gas in the circumnuclear region (~1.1x1.0 kpc^2) of the nearby Seyfert 1.8 galaxy NGC 1365, observed in the context of the Mid-IR Activity of Circumnuclear Line Emission (MIRACLE) program. We combined spatially resolved spectroscopic observations from JWST/MIRI, VLT/MUSE, and ALMA to investigate the ionized atomic gas and the warm and cold molecular phases. MIRI data revealed over 40 mid-IR emission lines from ionized and warm molecular gas. Moment maps show that both cold and warm molecular gas follow the rotation of the stellar disk along the circumnuclear ring. The ionized gas displays flux and kinematic patterns that depend on ionization potential (IP): low-IP species (<25 eV) trace the disk, while higher-IP lines (up to ~120 eV) trace outflowing material. The [O III]5700 and [Ne V]14 lines both trace the southeast nuclear outflow cone. Additionally, [Ne V]14 detects the northwest counter-cone, obscured in the optical and thus invisible in [O III]5700. Mid-IR diagnostics, unlike optical ones, clearly reveal the AGN as the primary ionization source in the nucleus. Emission from high-IP species is spatially coincident with the ionization cones and not with star-forming regions. Using the [Ne V]24/[Ne V]14 ratio, we derive an electron density of (750+-440) cm^(-3), in agreement with values from the [S II] optical doublet. For the first time, we apply a fully self-consistent approach combining advanced photoionization and kinematic models (HOMERUN+MOKA3D) to constrain intrinsic outflow properties, overcoming the limitations of simplified classical methods. Exploiting the synergy of JWST/MIRI and VLT/MUSE, HOMERUN reproduces fluxes of over 60 emission lines from optical to mid-IR, disentangling AGN and star formation contributions and yielding robust estimates of outflow mass, geometry, and energetics.

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arXiv2025

MARTA: Temperature-temperature relationships and strong-line metallicity calibrations from multiple auroral-line detections at cosmic noon

We present the first results from MARTA (Measuring Abundances at high Redshift with the T$_e$ Approach), a programme leveraging ultra-deep, medium-resolution JWST/NIRSpec spectroscopy to probe the interstellar medium (ISM) of star-forming galaxies at $z \sim 2 - 3$. We report detections of one or more auroral lines, including [O III]$\lambda4363$, [O II]$\lambda\lambda7320,7330$, [S II] $\lambda4068$, and [S III] $\lambda6312$ for 16 galaxies in the sample, providing measurements of multiple ionic temperatures. We tested the validity of the T[O II]-T[O III] relation at high redshift considering a total sample of 21 objects including literature data, and obtained a shallower slope than in the low-$z$ literature. However, such a slope is consistent with low-redshift data when ultra-low metallicity objects are considered. We assessed the correlation of the T[O II]-T[O III] relationship and its scatter on different physical parameters, finding a mild correlation with the ionisation parameter and radiation field hardness, while no significant correlation with gas density. The location of high-redshift data is also consistent with the low-$z$ literature in the T[O II]-T[S II], and T[S III]-T[O III] relations, although this conclusion is limited with low-number statistics. Finally, we leveraged our sample together with a comprehensive compilation of galaxies with [O III]$\lambda4363$ detections from the literature to recalibrate classical strong-line diagnostics at high redshift. MARTA represents a key addition in this space because it provides direct metallicities at moderately high oxygen abundances (12+log(O/H) $\sim8.0-8.4$).

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