arXiv subjects

Ignacio Trujillo

Publications and source records attributed to Ignacio Trujillo.

At least 19 recordsLinked to original sources

arXiv2026

Bridging integrated-light and resolved-star studies of Local Group dwarf spheroidals. A novel use of deep imaging based on amateur telescopes

Low-mass galaxies beyond the Local Group can only be studied through their integrated light, yet it remains unclear whether structural parameters inferred from integrated light are directly comparable to those obtained from resolved-star studies. Using new deep imaging obtained with small-aperture amateur telescopes, we analyse the classical dwarf spheroidals Leo II, Sculptor, and Fornax, whose stellar distributions have been extensively characterised through resolved-star studies. We find that the radial light distributions and effective radii inferred from integrated light are in excellent agreement with those derived from resolved stars, showing that resolved-star and integrated-light analyses can be placed within a common observational framework applicable across a broad range of distances. The two approaches are highly complementary: resolved-star analyses trace galaxies to very large radii but are limited by stellar crowding in their central regions, whereas integrated-light observations are insensitive to crowding and allow the inner stellar distribution to be traced to substantially smaller radii. The integrated-light analysis extends the structural analysis to radii up to an order of magnitude smaller than previous star-counting studies while significantly reducing the scatter in the measured profiles.

astro-ph.GA↗

arXiv2026

Ultra-Deep imaging of the starless galaxy candidate Cloud-9

We report the non-detection of stellar light associated with the dark galaxy candidate Cloud-9. Ultra-deep imaging obtained with HiPERCAM at the Gran Telescopio Canarias (GTC) reaches surface-brightness limits of 31.4 and 31.0 mag/arcsec$^2$ in g and r, respectively, approximately ten times deeper than previous deep imaging of the region. No stellar emission is detected within the central 1'$\times$1' ($\sim$1.3$\times$1.3 kpc) region of Cloud-9. Assuming an old, metal-poor stellar population, these limits imply a stellar surface mass density of no more than $\sim$0.01 M$_\odot$/pc$^2$ and an upper limit on the total stellar mass of 1.6$\times$10$^4$ M$_\odot$. This independent constraint from integrated light complements previous limits based on resolved-star counts and strengthens the case for Cloud-9 as a candidate starless galaxy.

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arXiv2026

Serendipitous discovery of an almost-dark galaxy in the Virgo Cluster

Analogues of extreme Local Group galaxies with very low surface brightnesses and large effective radii must exist elsewhere, still hidden due to current detection limits. We report the serendipitous discovery of the low-mass almost-dark galaxy TTT J1237327+143535 in the Virgo Cluster, observed using the Two-meter Twin Telescope at the Teide Observatory. TTT J1237327+143535 has a central surface brightness of $27.9 \pm 0.2 \, \mathrm{mag\, arcsec}^{-2}$ in the $g'$ band, an effective radius of $0.9 \pm 0.1 \mathrm{kpc}$, and a total stellar mass of $(2.2 \pm 0.4) \times 10^6 \mathrm{M_\odot}$. Its effective radius and absolute magnitude are similar to those of galaxies And XXI and And XXIII. The discovery of this extremely low-surface-brightness, extended, low-mass galaxy suggests the existence of a significant population of almost-dark galaxies in the Virgo Cluster. An in-depth analysis of the Next Generation Virgo Cluster Survey, as well as upcoming Rubin data releases and the 10-year Rubin Legacy Survey of Space and Time, is expected to reveal large samples of this extreme galaxy population, which will offer insights into galaxy formation in extreme conditions.

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arXiv2026

How large can galaxies be? Ultra-deep imaging of IC 1101, the most extended known galaxy

The maximum physical extent that galaxies can reach is poorly understood. In this regard, IC 1101, one of the most extended and massive galaxies known, provides a valuable opportunity to constrain the upper limit of galaxy sizes at the present epoch. Previous deep imaging of the system confirmed its enormous extension, but did not indicate whether it has an edge. We explore this issue using the deepest images ever taken of this galaxy; ultra-deep g- and r- band imaging from the INT/WFC, reaching {\mu} = 30 mag arcsec^-2 (3{\sigma} in an area equivalent to 10 x 10 arcsec^2). We model and subtract the scattered light from both stars and the galaxy itself using an extended PSF characterization and a hybrid wavelet-based deconvolution. Using a combination of surface brightness, colour, and stellar mass density profiles oriented at different position angles, we find that the main body of IC 1101 extends to Redge = 260 kpc along the semi-major axis (assuming the redshift of Abell 2029, z = 0.077), enclosing 3.4 x 10^12 M_sun in stars. This Redge is among the largest edge radii measured for any galaxy to date, placing IC 1101 at the extreme upper end of the mass-size relation. In addition, we report a large number of asymmetrical, very low surface brightness features around the galaxy that are spatially consistent with the large-scale disturbances observed in the intracluster medium through X-ray studies of the Abell 2029 cluster, in which IC 1101 is embedded. With a confirmed diameter of around 520 kpc, IC 1101 stands as the largest galaxy known to date; yet, its outskirts show clear signatures of ongoing mass assembly, indicating that its spatial extent is still growing.

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arXiv2026

The explosive growth of the Messier 74 galaxy. A galaxy doubling its size in less than a Gigayear

Galaxy formation models predict that galaxies grow inside-out, becoming larger over time. While observations broadly support this paradigm, the nature and timescales of this growth remain poorly constrained. We report the discovery of an extremely faint and young (~600 Myr) stellar component in the outer regions of the nearby galaxy Messier 74 (M74). Using deep optical imaging from the TST telescope at the Teide Observatory, reaching surface brightness limits of ~30-31.5 mag arcsec^-2 in the g, r and i bands, we detect stellar emission extending well beyond the previously known disc radius of ~14 kpc. This newly identified component reaches galactocentric distances of ~30 kpc, effectively doubling the known size of the stellar disc and matching the extent of the HI disc. The revised size of M74 places it in the upper envelope of the mass-size relations. The young age of the outer stellar population suggests a recent episode of disc growth, potentially occurring on timescales shorter than ~1 Gyr. We discuss a possible scenario in which a past flyby interaction with UGC 1176 may have triggered this extended star formation. Further studies of galaxies with similar deep imaging will be key to determining whether such rapid outer disc growth is common or exceptional.

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arXiv2026

Witnessing the rapid growth of disk galaxies over cosmic time using JWST and HST

Measuring galaxy sizes is fundamental to understanding how galaxies grow and evolve. Traditional methods to measure sizes either trace the concentration of light (i.e., effective radius) or are limited by the depth of the survey (isophotal methods). With the advent of deep, wide surveys, a new physically motivated definition of size has emerged: the edge of the galaxy, defined as the most distant location where star formation has occurred or is still occurring. In this work, we take advantage of the extraordinary depth and spatial resolution of the Hubble and James Webb Space Telescopes to perform an accurate study of galaxy edges at $z=1$. Using 22 photometric bands, we derive radial age and metallicity profiles for two disk galaxies in the GOODS-South field with stellar masses of around $4\times10^{10}\ M_\odot$. The age profiles display a characteristic U-shape, while the metallicity profiles steadily decrease with galactocentric distance. The turnover in the age profile occurs near the galaxy edge, suggesting that stellar migration is responsible for the stars beyond the edge of these galaxies. Comparison with $z=0$ disk galaxies suggests that galaxies at $z=1$ grow inside-out, with little or no increase in mass within the inner 8 kpc, but a significant increase (approximately 300\%) in the outer regions.

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arXiv2026

LIGHTS. The Thin Encircling Stellar Stream of NGC 3938

We present a stellar stream found in images of the nearby, nearly face-on, late-type galaxy, NGC 3938 obtained for the LBT Imaging of Galactic Halos and Tidal Structures (LIGHTS) survey that is thin, has very low mean surface brightness ($\langle\mu_g\rangle \approx$ 28.7 mag arcsec$^{-2}$ and $\langle\mu_r\rangle \approx$ 28.1 mag arcsec$^{-2}$), appears to lie nearly on the plane of the sky, and wraps more than half way around a host galaxy that is otherwise apparently isolated. We estimate that the progenitor had a stellar mass of $\sim 3.7\times 10^7$ M$_\odot$. Despite an intriguing apparent offset between the centroid of the host galaxy and the apparent center of the stream orbit, we find that we can reproduce the morphology, including this apparent off-centering, with simple models and standard assumptions about the host (thin disk centered within a canonical spherical dark matter halo) and the progenitor satellite orbit. We identify a number of detailed features of the stream, such as changes in curvature and density, that will require more complex models to reproduce. Even this rather simple system provides a rich set of constraints with which to explore the accretion history and gravitational potential of an otherwise unremarkable late-type galaxy. Given the depth of the LIGHTS images, this system is an example of the types of stellar stream that could be found in a majority of nearby giant galaxies with the 10-year stack of Rubin/LSST data.

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arXiv2026

JWST spectra are consistent with the edge-on star-forming galaxy scenario for the "runaway supermassive black hole"

The linear structure reported by van Dokkum et al. (2023) has been proposed as either a massive stellar wake produced by a runaway supermassive black hole (SMBH) or a bulgeless edge-on galaxy. New JWST/NIRSpec IFU observations target the tip of the structure, where a SMBH would produce a bow shock, whereas a normal galaxy would host an HII region. Using standard BPT diagrams ([OIII]5007/Hb vs [NII]6583/Ha and [OIII]5007/Hb vs [OII]6716,6731/Ha), we find that the line ratios at the tip fall on the locus of low-metallicity low-extinction HII regions. This region does not overlap with loci typical of shocks in merging galaxies. Thus, these results are consistent with the interpretation that the linear structure is a star-forming galaxy, with the bright knot representing one of its HII regions.

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arXiv2025

Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: A Low Surface Brightness Science Case

The Extragalactic Low Surface Brightness (LSB, $\mu_V\gtrsim 27$ mag/arcsec$^2$) Universe represents a crucial, yet largely unseen, frontier in modern astrophysics. This faint realm holds the keys to completing our understanding of galaxy evolution, hierarchical assembly, and even the fundamental nature of dark matter. Our current theoretical models are inherently incomplete, largely mirroring the properties of the brightest, most easily observed objects. To overcome this critical bias and unlock the secrets of this realm, a transformative leap in observational capability is required. A 30 to 40m class telescope, leveraging unprecedented sensitivity and spatial resolution, especially with adaptive optics, is the essential tool to fundamentally probe these faint, low-density stellar regimes. This white paper details the transformative LSB science that such a facility, strategically positioned in the Northern Hemisphere (NH) to access crucial nearby structures and rich environments, can achieve.

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arXiv2025

The mysterious Globular Cluster population of MATLAS-2019

MATLAS-2019 (also known as NGC5846-UDG1) has attracted significant attention due to the ongoing debate surrounding its Globular Cluster (GC) population, with several studies addressing the issue yet reaching little consensus. In this paper we take advantage of HST's multi-wavelength coverage (F475W, F606W and F814W observations) with the addition of deep u-band imaging from Gran Telescopio de Canarias, to perform the most detailed study and estimation to date of the GC population of the ultra-diffuse galaxy MATLAS-2019. The improved constraints provided by the combination of high spatial resolution and better coverage of the GC spectral energy distribution has allowed us to obtain a clean sample of GCs in this galaxy. We report a number of 33+-3 GCs in MATLAS-2019, supporting the previous lower estimates for this galaxy. The GC population of this galaxy is highly concentrated with ~80% of the GCs inside the effective radius (Re) of the galaxy and the GC half-number radius Re,GC is 0.7Re. Using the GC-Halo mass relation, we estimate a halo mass for MATLAS-2019 of (1.14+-0.1)x10**11 solar masses. The GC luminosity function and the distribution of effective radii of the GCs favour a distance to the galaxy of 20.0+-0.9 Mpc. In agreement with previous findings, we find that the distribution of GCs is highly asymmetric even though the distribution of stars in the galaxy is symmetric. This suggests that assumptions about the symmetry of the GC distribution may be incorrect when used to calculate the number of GCs with such low statistics.

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arXiv2025

Deep imaging of the very isolated dwarf galaxy NGC6789

We present deep optical imaging of the extremely isolated dwarf galaxy NGC 6789, obtained with the new 2-meter Two-meter Twin Telescope (TTT3) at Teide Observatory. Despite its location in the Local Void, NGC 6789 exhibits surprising recent central star formation equivalent to approximately 4% of its total stellar mass. The origin of the gas necessary for this level of star formation remains unknown. Our data reach surface brightness limits of 29.8, 29.4, and 28.9 mag arcsec$^{-2}$ in the Sloan g, r, and i filters, respectively, and reveal no evidence of tidal features or merger remnants down to $\sim$30 mag arcsec$^{-2}$ (or equivalently, at a radial distance larger than 1.6 kpc). The galaxy's undisturbed outer elliptical morphology suggests that its recent central star formation was likely produced by either in-situ residual gas or by the accretion of external pristine gas not associated with a minor merging activity.

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arXiv2025

Revisiting the structure of galactic disks with deep imaging

Thanks to new advances in astronomical imaging, we can now routinely explore disk galaxy profiles about two magnitudes deeper than the data available 20 years ago. In this regard, it is an opportune time to reevaluate the past classifications of different surface brightness Types. In this paper, we explore the stellar mass profiles of a sample of disk galaxies with similar stellar masses ($\sim$10$^{10}$ M$_{\odot}$) using IAC Stripe82 Legacy Project data. We find that Type I, II-CT, and III-d galaxies exhibit edges at surface brightnesses $\mu_g$(R$_{edge}$)$\sim$26.5 mag/arcsec$^2$ and surface mass densities $\Sigma$(R$_{edge}$)$\sim$0.5-1 M$_{\odot}$/pc$^2$. These surface brightnesses were outside the range of typical SDSS images and, therefore, unstudied. The present data suggest (although the statistics are inconclusive) that the main difference between the previous profile Types is the presence of either a more or a less intense bulge. Half of the Type II-CT galaxies are Sc, whereas half of the Type III-d galaxies are Sb. Finally, Type III-d galaxies have low mass surface density disks ($\Sigma$($\Delta$ $R_{\mathrm{exp}}$)$\sim$0.5 M$_{\odot}$/pc$^2$) and are bluer $(g-r)_0$=0.32$\pm$0.02 than the other Types ($(g-r)_0$=0.42$\pm$0.02 for Type I and II-CT), suggesting that their disks probably formed later in time.

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arXiv2025

An accurate measure of the size of dark matter halos using the size of galaxies

The physically motivated definition of galaxy size proposed recently, linked to the farther location of the in situ star formation, considerably reduces the scatter of the galaxy mass-size relation and provides a viable method to infer the galaxy stellar mass from its size. We provide a similar relation correlating the size of galaxies with the size of their dark matter haloes by leveraging the small scatter of the aforementioned relation. We analysed the simulated galaxies of the two main cosmological volumes of the EAGLE simulations and computed the size of the galaxies and their mass when mimicking the observational analysis. For central galaxies, we computed the relation between galaxy size and halo size. We show that the simulated galaxies reproduce the observed stellar mass-size relation's normalisation and slope. The scatter of this relation, 0.06 dex, matches the intrinsic scatter measured in observation. We then computed the correlation between galaxy size and halo size and found that the relation is steeper than when using the half-mass radius as a measure of size, with the scatter (0.1 dex) being a factor of two smaller than the observed relation. As well, the galaxy-to-halo mass relation derived from the simulations provides a factor of two better scatter than the observed scatter. This opens the possibility of measuring the size of dark matter haloes with greater accuracy (less than 50%, i.e. around six times better than using the effective radius) by using only deep imaging data.

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arXiv2025

The slow evolution of dark matter halos from cusp to core naturally produces extended stellar core-like distributions

Motivated by the observation of extended stellar cores in dark matter (DM) dominated dwarf galaxies, this study investigates a simple mechanism by which stellar cores can form as a result of DM halo expansion. Several non-CDM models predict that the DM distribution thermalizes over time, transforming initially cuspy halos into cores. This transformation weakens the gravitational potential, allowing the stellar component to expand and form diffuse, core-like structures. Using analytical models and adiabatic invariants, we examine stellar systems with purely tangential, purely radial, and isotropic orbits evolving under a slowly changing potential. Across a wide range of initial and final conditions, we find that stellar cores form relatively easily, though their properties depend sensitively on these conditions. Orbit types preserve their nature during the DM halo expansion: tangential and radial orbits remain so, while isotropic orbits remain nearly isotropic in the central regions. Systems with circular orbits develop stellar cores when the initial stellar density logarithmic slope lies between -0.5 and -1.2, whereas radial systems do not form cores. Isotropic systems behave similarly to tangential ones, producing cores that are isotropic in the center but develop increasing radial anisotropy outward; the anisotropy parameter "beta" grows from sim 0.07 at the core radius to sim 0.5 at three core radii. The theoretical and observational literature suggests initial DM profiles with steep slopes and stellar distributions that are shallower and isotropic at the center. Given these conditions, the mechanism predicts stellar cores with radii at least 40 % that of the DM core and inner logarithmic slopes shallower than 0.6.

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arXiv2025

Deep imaging of the galaxy Malin 2 shows new faint structures and a candidate satellite dwarf galaxy

Giant Low Surface Brightness (GLSB) galaxies are extreme disk systems with exceptionally large sizes and low stellar densities. Their formation and evolution remain poorly constrained due to the challenges of detecting their faint disks. We present deep, multi-band optical imaging of Malin 2, a prototypical GLSB galaxy, with the newly commissioned Two-meter Twin Telescope (TTT) at the Teide Observatory. Our $g$, $r$, and $i$-band data reach surface brightness depths of 30.3, 29.5, and 28.2 mag arcsec$^{-2}$ (3$\sigma$, $10^{\prime\prime} \times 10^{\prime\prime}$), tracing the stellar disk of Malin 2 to $\sim$110 kpc. We detect new diffuse structures, including a prominent emission in the northwest coincident with the HI distribution, and a faint spiral arm-like feature in the southeast. We also identify a very faint dwarf galaxy, TTT-d1 ($\mu_{0,g} \sim 26$ mag arcsec$^{-2}$), about 130 kpc southeast of Malin 2, possibly its first known satellite ultra-diffuse galaxy. A multi-directional wedge photometric analysis of Malin 2 shows strong azimuthal variations in its stellar disk. Compared with nearby spirals and other GLSBs, Malin 2 lies at the extreme end in radial extent and stellar mass surface density. The overlap between the asymmetric stellar emission and a lopsided HI distribution suggests contributions from tidal interactions in the formation of the giant disk of Malin 2. Our results highlight the importance of ultra-deep, wide-field imaging in understanding the structural complexity of giant LSB galaxies. Upcoming surveys such as LSST will be crucial to determine whether the features we observe in Malin 2 are common to other giant LSB disk galaxies.

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arXiv2025

NASIM: Revealing the low surface brightness Universe from legacy VISTA data

Near-infrared imaging is a powerful technique in observational astronomy, but the bright background, primarily from the Earth\'s atmosphere, makes the detection of faint features particularly challenging. To recover low surface brightness (LSB) structures in such data, we present NASIM (Near-infrared Automated low Surface brightness reduction In Maneage), a fully automated and reproducible data reduction pipeline optimised for VISTA/VIRCAM observations. NASIM builds on GNU Astronomy Utilities (Gnuastro) to effectively remove large-scale instrumental artefacts while preserving faint, diffuse emission. As a key science application, we focus on deep Ks-band observations of the Euclid Deep Field South (KEDFS), one of the deepest VISTA/VIRCAM datasets and a high-priority field for synergy with current and future facilities, including Euclid, JWST, LSST, Roman, Spitzer, and ALMA. With VIRCAM no longer operational, KEDFS now stands as a unique legacy dataset. We release selected tiles from the KEDFS survey and highlight science cases, including galaxy outskirts, LSB galaxies, and intracluster light, that demonstrate NASIM\'s ability to recover diffuse structures. A direct comparison with conventional VISTA data reduction pipelines demonstrates the advantages of NASIM in preserving diffuse emission without compromising compact source detection. All quantitative results presented in this paper are fully reproducible with Maneage (commit 4d32667).

astro-ph.IM↗

arXiv2025

LIGHTS. A robust technique to identify galaxy edges

The LIGHTS survey is imaging galaxies at a depth and spatial resolution comparable to what the Legacy Survey of Space and Time (LSST) will produce in 10 years (i.e., $\sim$31 mag/arcsec$^2$; 3$\sigma$ in areas equivalent to 10$^{\prime\prime}$$\times$ 10$^{\prime\prime}$). This opens up the possibility of probing the edge of galaxies, as the farthest location of in-situ star formation, with a precision that we have been unable to achieve in the past. Traditionally, galaxy edges have been analyzed in one-dimension through ellipse averaging or visual inspection. Our approach allows for a two-dimensional exploration of galaxy edges, which is crucial for understanding deviations from disc symmetry and the environmental effects on galaxy growth. In this paper, we propose a novel method using the second derivative of the surface mass density map of a galaxy to determine its edges. This offers a robust quantitative alternative to traditional edge-detection methods when deep imaging is available. Our technique incorporates Wiener-Hunt deconvolution to remove the effect of the Point Spread Function (PSF) by the galaxy itself. By applying our methodology to the LIGHTS galaxy NGC 3486, we identify the edge at 205$^{\prime\prime}$ $\pm$ 5$^{\prime\prime}$. At this radius, the stellar surface mass density is $\sim$1 M$_\odot$/pc$^2$, supporting a potential connection between galaxy edges and a threshold for in-situ star formation. Our two-dimensional analysis on NGC 3486 reveals an edge asymmetry of $\sim$5$\%$. These techniques will be of paramount importance for a physically motivated determination of the sizes of galaxies in ultra-deep surveys such as LSST, Euclid and Roman.

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arXiv2025

A targeted, parallax-based search for Planet Nine

The hypothesized Planet Nine is thought to reside in the distant outer solar system, potentially explaining various anomalies in the orbits of extreme trans-Neptunian objects (ETNOs). In this work, we present a targeted observational search for Planet Nine in a field of approximately 98 square-degrees. This field is close to the highest probability region of finding Planet Nine, according to simulations, but poorly constrained by previous searches. Our observations and search methodology, based on the detection of parallax position shifts between consecutive nights, work well in these conditions. We provide 85% confidence exclusion limits for objects with Sloan r-band magnitudes brighter than between 21.0 and 21.4, with an average sensitivity limit of 21.3. No credible Planet Nine candidates were identified within this field and magnitude limits. A caveat to our approach is that it would miss a candidate if its position were affected by scattered light from bright stars in at least one of the nights. However, we estimate that the probability for this is very low, around 0.4%. We discuss several possible reasons for our Planet Nine non-detection. Our study complements prior searches, particularly those using archival survey data that are limited in the Galactic plane or at fainter brightness limits. While our consecutive-night observation approach offers high sensitivity to minimal motion, extending the search for Planet Nine to fainter magnitudes (which may be crucial, according to recent predictions), will require higher sensitivity instrumentation

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