arXiv subjects

Ignacio Trujillo

Publications and source records attributed to Ignacio Trujillo.

At least 55 records · Page 3Linked to original sources

arXiv2023

Super-massive black hole wake or bulgeless edge-on galaxy?

van Dokkum et al. (2023) reported the serendipitous discovery of a thin linear object interpreted as the trail of star-forming regions left behind by a runaway supermassive black hole (SMBH) kicked out from the center of a galaxy. Despite the undeniable interest in the idea, the actual physical interpretation is not devoid of difficulty. The wake of a SMBH produces only small perturbations on the external medium, which has to be in exceptional physical conditions to collapse gravitationally and form a long (40 kpc) massive (3e9 Msun) stellar trace in only 39 Myr. Here we offer a more conventional explanation: the stellar trail is a bulgeless galaxy viewed edge-on. This interpretation is supported by the fact that its position--velocity curve resembles a rotation curve which, together with its stellar mass, puts the object right on top of the Tully-Fisher relation characteristic of disk galaxies. Moreover, the rotation curve (Vmax sim 110 km/s), stellar mass, extension, width (z0 sim 1.2 kpc), and surface brightness profile of the object are very much like those of IC5249, a well-known local bulgeless edge-on galaxy. These observational facts are difficult to interpret within the SMBH wake scenario. We discuss in detail the pros and cons of the two options.

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arXiv2022

A new era of intracluster light studies with JWST

Still largely unexplored, the diffuse light in cluster of galaxies traces the past and on-going buildup of these massive structures. Here, we present the first comprehensive study of the intracluster light (ICL) of the cluster SMACS-J0723.3-7327 (z=0.39) using the JWST Early Release Observations. These deep and high spatial resolution images allow the study of the ICL with high signal-to-noise ratio up to a radial distance of $\sim400$ kpc, twice as far with respect to previous HST studies of intermediate redshift clusters. This opens up the possibility of exploring the rich mixture of processes that are building the ICL. We find that the inner parts (R$<$100 kpc) are built through a major merger while the outer parts (R$>$ 100 kpc) are mainly produced by the tidal stripping of Milky Way-like satellites. We also found that the slope of the stellar mass density radial profile of the ICL of this cluster ($α_{3D} = -2.47\pm0.13$) follows closely the predicted dark matter halo slope ($α_{3D\mathrm{,DM}} = -2.6$ to $-2$), supporting the idea that both components have a similar shape and thus the potential of using the ICL as a tracer of the dark matter distribution in clusters of galaxies. Future JWST studies of the ICL are set to revolutionise our understanding of cluster formation and will be crucial to improve the gravitational lensing mass maps of these structures and thus to accurately characterise the properties of the first galaxies.

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arXiv2022

Implications for Galaxy Formation Models from Observations of Globular Clusters around Ultra-Diffuse Galaxies

We present an analysis of Hubble Space Telescope observations of globular clusters (GCs) in six ultra-diffuse galaxies (UDGs) in the Coma cluster, a sample that represents UDGs with large effective radii ($R_{\rm e}$), and use the results to evaluate competing formation models. We eliminate two significant sources of systematic uncertainty in the determination of the number of GCs, $N_{\rm GC}$ by using sufficiently deep observations that (i) reach the turnover of the GC luminosity function and (ii) provide a sufficient number of GCs with which to measure the GC number radial distribution. We find that $N_{\rm GC}$ for these galaxies is on average $\sim$20, which implies an average total mass, $M_{\rm total}$, $\sim$ $10^{11}$ $M_{\odot}$ when applying the relation between $N_{\rm GC}$ and $M_{\rm total}$. This value of $N_{\rm GC}$ lies at the upper end of the range observed for dwarf galaxies of the same stellar mass and is roughly a factor of two larger than the mean. The GC luminosity function, radial profile and average colour are more consistent with those observed for dwarf galaxies than with those observed for the more massive ($L^*$) galaxies, while both the radial and azimuthal GC distributions closely follow those of the stars in the host galaxy. Finally, we discuss why our observations, specifically the GC number and GC distribution around these six UDGs, pose challenges for several of the currently favoured UDG formation models.

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arXiv2021

Introducing the LBT Imaging of Galactic Halos and Tidal Structures (LIGHTS) survey. A preview of the low surface brightness Universe to be unveiled by LSST

We present the first results of the LBT Imaging of Galaxy Haloes and Tidal Structures (LIGHTS) survey. LIGHTS is an ongoing observational campaign with the 2x8.4m Large Binocular Telescope (LBT) aiming to explore the stellar haloes and the low surface brightness population of satellites down to a depth of muV~31 mag/arcsec^2 (3 sigma in 10"x10" boxes) of nearby galaxies. We simultaneously collected deep imaging in the g and r Sloan filters using the Large Binocular Cameras (LBCs). The resulting images are 60 times (i.e. ~4.5 mag) deeper than those from the Sloan Digital Sky Survey (SDSS), and they have characteristics comparable (in depth and spatial resolution) to the ones expected from the future Legacy Survey of Space and Time (LSST). Here we show the first results of our pilot programme targeting NGC1042 (an M33 analogue at a distance of 13.5 Mpc) and its surroundings. The depth of the images allowed us to detect an asymmetric stellar halo in the outskirts of this galaxy whose mass (1.4+-0.4x10^8 Msun) is in agreement with the Lambda Cold Dark Matter (LambdaCDM) expectations. Additionally, we show that deep imaging from the LBT reveals low mass satellites (a few times 10^5 Msun) with very faint central surface brightness muV(0)~27 mag/arcsec^2 (i.e. similar to Local Group dwarf spheroidals, such as Andromeda XIV or Sextans, but at distances well beyond the local volume). The depth and spatial resolution provided by the LIGHTS survey open up a unique opportunity to explore the `missing satellites' problem in a large variety of galaxies beyond our Local Group down to masses where the difference between the theory and observation (if any) should be significant.

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arXiv2021

A disk and no signatures of tidal distortion in the galaxy "lacking" dark matter NGC 1052-DF2

Using ultra-deep imaging ($μ_g = 30.4$ mag/arcsec$^2$; 3$σ$, 10"x10"), we probed the surroundings of the first galaxy "lacking" dark matter KKS2000[04] (NGC 1052-DF2). Signs of tidal stripping in this galaxy would explain its claimed low content of dark matter. However, we find no evidence of tidal tails. In fact, the galaxy remains undisturbed down to a radial distance of 80 arcsec. This radial distance triples previous spatial explorations of the stellar distribution of this galaxy. In addition, the distribution of its globular clusters (GCs) is not extended in relation to the bulk of the galaxy (the radius containing half of the GCs is 21 arcsec). We also found that the surface brightness radial profiles of this galaxy in the g and r bands decline exponentially from 35 to 80 arcsec. That, together with a constant ellipticity and position angle in the outer parts of the galaxy strongly suggests the presence of a low-inclination disk. This is consistent with the evidence of rotation found for this object. This finding implies that the dynamical mass of this galaxy is a factor of 2 higher than previously reported, bringing the dark matter content of this galaxy in line with galaxies of similar stellar mass.

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arXiv2021

Numerical simulations of dark matter haloes produce polytropic central cores when reaching thermodynamic equilibrium

Self-gravitating astronomical objects often show a central plateau in the density profile (core) whose physical origin is hotly debated. Cores are theoretically expected in N-body systems of maximum entropy, however, they are not present in the canonical N-body numerical simulations of cold dark matter (CDM). Our work shows that despite this apparent contradiction between theory and numerical simulations, they are fully consistent. Simply put, cores are characteristic of systems in thermodynamic equilibrium, but thermalizing collisions are purposely suppressed in CDM simulations. When collisions are allowed, N-body numerical simulations develop cored density profiles, in perfect agreement with the theoretical expectation. We compare theory and two types of numerical simulations: (1) when DM particles are self-interacting (SIDM) with enough cross-section, then the effective two-body relaxation timescale becomes shorter than the Hubble time resulting in cored DM haloes. The haloes thus obtained, with masses from dwarf galaxies to galaxy clusters, collapse to a single shape after normalization, and this shape agrees with the polytropic density profile theoretically expected. (2) The inner radii in canonical N-body numerical simulations are always discarded because the use of finite-mass DM particles artificially increases the two-body collision rate. We show that the discarded radii develop cores that are larger than the employed numerical softening and have polytropic shapes independently of halo mass. Our work suggests that the presence of cores in simulated (or observed) density profiles can used as evidence for systems in thermodynamic equilibrium.

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arXiv2020

Galactic cirri in deep optical imaging

The presence of Galactic cirri in deep optical observations is one of the most challenging problems that the extragalactic community is already facing, and it is expected to be even tougher in the near future with the increasing depth of optical surveys. To address this problem, we have performed a photometric characterization of Galactic cirri in the IAC Stripe82 Legacy Survey using g, r, i and z SDSS bands. Through comprehensive image processing techniques we show that, in most cases, the colors of the cirri differ significantly from the colors of extragalactic sources. This could be a promising way to discern extragalactic features from dust of the Milky-Way. We suggest that the use of multi-band and ultra-deep optical photometry produced by the Large Synoptic Survey Telescope will be very efficient in detecting the Galactic dust with a higher spatial resolution than those provided by far infrared observations.

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arXiv2020

Galactic cirri in deep optical imaging

The ubiquitous presence of Galactic cirri in deep optical images represents a major obstacle to study the low surface brightness features of extragalactic sources. To address this issue, we have explored the optical properties of cirri using g, r, i and z bands in the Sloan Digital Sky Survey (SDSS) Stripe82 region. Using state-of-the-art, custom made, image processing techniques, including the modeling and removal of the instrumental scattered light produced by the stars, we managed to isolate the optical diffuse emission by the cirri, allowing their photometric characterization. We find that their optical colors are driven by the dust column density: The cirri become redder as their 100 $μ$m emission increases. Remarkably, the optical colors of the Galactic cirri differ significantly from those of extragalactic sources, with a characteristic bluer r-i color for a given g-r, allowing one to detect these by using a simple color relation. Our results show the high potential of deep multi-band optical photometry, on its own, identifying the presence of cirri at a higher spatial resolution than those provided by far-infrared observations. The combination of very deep data and multi-band photometry (as the one produced by LSST and Euclid) would make it possible to build dust maps of unprecedented quality.

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arXiv2020

The galaxy "missing dark matter" NGC1052-DF4 is undergoing tidal disruption

The existence of long-lived galaxies lacking dark matter represents a challenge to our understanding of how galaxies form. Here, we present evidence that explains the lack of dark matter in one of such galaxies: NGC1052-DF4. Deep optical imaging of the system has detected tidal tails in this object caused by its interaction with its neighbouring galaxy NGC1035. As stars are more centrally concentrated than the dark matter, the tidal stripping will remove a significant percentage of the dark matter before affecting the stars of the galaxy. Only ~7% of the stellar mass of the galaxy is in the tidal tails, suggesting that the stars of NGC1052-DF4 are starting only now to be affected by the interaction, while the percentage of remaining dark matter is <1%. This naturally explains the low content of dark matter inferred for this galaxy and reconciles these type of galaxies with our current models of galaxy formation.

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arXiv2020

The number of globular clusters around the iconic UDG DF44 is as expected for dwarf galaxies

There is a growing consensus that the vast majority of ultra-diffuse galaxies (UDGs) are dwarf galaxies. However, there remain a few UDGs that seem to be special in terms of their globular cluster (GC) systems. In particular, according to some authors, certain UDGs exhibit large GC populations when compared to expectations from their stellar (or total) mass. Among these special UDGs, DF44 in the Coma cluster is one of the better-known examples. DF44 has been claimed to have a relatively high number of GCs, $N_{GC}=74^{+18}_{-18}$, for a stellar mass of only $3\times 10^8$ $M_{ \odot }$ which would indicate a much larger dark halo mass than dwarfs of similar stellar mass. In this paper we revisit this number and, contrary to previous results, find $N_{GC}=21^{+7}_{-9}$ assuming that the distribution of the GCs follows the same geometry as the galaxy. If we assume that the GCs around DF44 are distributed in a (projected) circularly symmetric way and, if we use a less strict criterion for the selection of the GCs, we find $N_{GC}=18^{+23}_{-12}$. Making use of the $M_{\rm GC} - M_{\rm halo}$ relation, this number of GCs suggests a dark matter halo mass of $M_{halo}=1.1^{+0.4}_{-0.5} \times 10^{11} M_{\odot}$, a value which is consistent with the expected total mass for DF44 based on its velocity dispersion, $σ=33^{+3}_{-3}$ km s$^{-1}$. We conclude that the number of GCs around DF44 is as expected for regular dwarf galaxies of similar stellar mass and DF44 is not extraordinary in this respect.

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arXiv2020

The principle of maximum entropy explains the cores observed in the mass distribution of dwarf galaxies

Cold Dark Matter (CDM) simulations predict a central cusp in the mass distribution of galaxies. This prediction is in stark contrast with observations of dwarf galaxies which show a central plateau or 'core' in their density distribution. The proposed solutions to this core-cusp problem can be classified into two types. Either they invoke feedback mechanisms produced by the baryonic component of the galaxies, or they assume the properties of the dark matter (DM) particle to depart from the CDM hypothesis. Here we propose an alternative yet complementary explanation. We argue that cores are unavoidable in the self-gravitating systems of maximum entropy resulting from non-extensive statistical mechanics. Their structure follows from the Tsallis entropy, suitable for systems with long-range interactions. Strikingly, the mass density profiles predicted by such thermodynamic equilibrium match the observed cores without any adjustment or tuning. Thus, the principle of maximum Tsallis entropy explains the presence of cores in dwarf galaxies.

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arXiv2020

Reconstructing the mass accretion histories of nearby Red Nuggets with their globular cluster systems

It is generally recognized that massive galaxies form through a combination of in-situ collapse and ex-situ accretion. The in-situ component forms early, where gas collapse and compaction leads to the formation of massive compact systems (blue and red "nuggets") seen at $z>1$. The subsequent accretion of satellites brings in ex-situ material, growing these nuggets in size and mass to appear as the massive early-type galaxies (ETGs) we see locally. Due to stochasticity in the accretion process, in a few rare cases a red nugget will evolve to the present day having undergone little ex-situ mass accretion. The resulting massive, compact and ancient objects have been termed "relic galaxies". Detailed stellar population and kinematic analyses are required to characterise these systems. However, an additional crucial aspect lies in determining the fraction of ex-situ mass they have accreted since their formation. Globular cluster systems can be used to constrain this fraction, since the oldest and most metal-poor globular clusters in massive galaxies are primarily an accreted, ex-situ population. Models for the formation of relic galaxies and their globular cluster systems suggest that, due to their early compaction and limited accretion of dark-matter dominated satellites, relic galaxies should have characteristically low dark-matter mass fractions compared to ETGs of the same stellar mass.

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arXiv2020

The Sloan Digital Sky Survey extended point spread functions

A robust and extended characterization of the point spread function (PSF) is crucial to extract the photometric information produced by deep imaging surveys. Here, we present the extended PSFs of the Sloan Digital Sky Survey (SDSS), one of the most productive astronomical surveys of all time. By stacking ~1000 images of individual stars with different brightness, we obtain the bidimensional SDSS PSFs extending over 8 arcmin in radius for all the SDSS filters(u, g, r, i, z). This new characterization of the SDSS PSFs is near a factor of 10 larger in extension than previous PSFs characterizations of the same survey. We found asymmetries in the shape of the PSFs caused by the drift scanning observing mode. The flux of the PSFs is larger along the drift scanning direction. Finally, we illustrate with an example how the PSF models can be used to remove the scattered light field produced by the brightest stars in the central region of the Coma cluster field. This particular example shows the huge importance of PSFs in the study of the low-surface brightness Universe, especially with the upcoming of ultradeep surveys, such as the Large Synoptic Survey Telescope (LSST). Following a reproducible science philosophy, we make all the PSF models and the scripts used to do the analysis of this paper publicly available (snapshot v0.5-0-g62d83df).

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arXiv2020

A physically motivated definition for the size of galaxies in an era of ultra-deep imaging

Present-day multi-wavelength deep imaging surveys allow to characterise the outskirts of galaxies with unprecedented precision. Taking advantage of this situation, we define a new physically motivated measurement of size for galaxies based on the expected location of the gas density threshold for star formation. Employing both theoretical and observational arguments, we use the stellar mass density contour at 1 $M_{\rm \odot}$ pc$^{-2}$ as a proxy for this density threshold for star formation. This choice makes our size definition operative. With this new size measure, the intrinsic scatter of the global stellar mass ($M_{\rm \star}$) - size relation (explored over five orders of magnitude in stellar mass) decreases to $\sim$0.06 dex. This value is 2.5 times smaller than the scatter measured using the effective radius ($\sim$0.15 dex) and between 1.5 and 1.8 times smaller than those using other traditional size indicators such as $R_{\rm 23.5,i}$ ($\sim$0.09 dex), the Holmberg radius $R_{\rm H}$ ($\sim$0.09 dex) and the half-mass radius $R_{\rm e,M_{\star}}$ ($\sim$0.11 dex). Moreover, galaxies with 10$^7$ $M_{\rm \odot} <$ $M_{\star} < 10^{11}$ $M_{\rm \odot}$ increase monotonically in size following a power-law with a slope very close to 1/3, equivalent to an average stellar mass 3D density of $\sim$4.5$\times$10$^{-3}$ $M_{\rm \odot}$ pc$^{-3}$ for galaxies within this mass range. Galaxies with $M_{\rm \star}$$>$10$^{11}$ $M_{\rm \odot}$ show a different slope with stellar mass, which is suggestive of a larger gas density threshold for star formation at the epoch when their star formation peaks.

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arXiv2020

Are ultra-diffuse galaxies Milky Way-sized?

Now almost 70 years since its introduction, the effective or half-light radius has become a very popular choice for characterising galaxy size. However, the effective radius measures the concentration of light within galaxies and thus does not capture the intuitive definition of size which is related to the edge or boundary of objects. For this reason, we aim to demonstrate the undesirable consequence of using the effective radius to draw conclusions about the nature of faint 'ultra-diffuse galaxies' (UDGs) when compared to dwarfs and Milky Way-like galaxies. Instead of the effective radius, we use a measure of galaxy size based on the location of the gas density threshold required for star formation. Compared to the effective radius, this physically motivated definition places the sizes much closer to the boundary of a galaxy. Therefore, considering the sizes and stellar mass density profiles of UDGs and regular dwarfs, we find that the UDGs have sizes that are within the size range of dwarfs. We also show that currently known UDGs do not have sizes comparable to Milky Way-like objects. We find that, on average, UDGs are ten times smaller in extension than Milky Way-like galaxies. These results show that the use of size estimators sensitive to the concentration of light can lead to misleading results.

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arXiv2019

The TRGB distance to the second galaxy "missing dark matter". Evidence for two groups of galaxies at 13.5 and 19 Mpc in the line of sight of NGC1052

A second galaxy ``missing dark matter" (NGC1052-DF4) has been recently reported. Here we show, using the location of the Tip of the Red Giant Branch (TRGB), that the distance to this galaxy is 14.2+-0.7 Mpc. This locates the galaxy 6 Mpc closer than previously determined. We also analyse the distances to the brightest galaxies in the field-of-view (FOV) of NGC1052. We find this field is populated by two groups of galaxies in projection: one dominated by NGC1052 and NGC1047 at ~19 Mpc and another group containing NGC1042 and NGC1035 (as well as [KKS2000]04 and NGC1052-DF4) at ~13.5 Mpc. At a distance of 13.5 Mpc the globular clusters of NGC1052-DF4 have the same properties than globular clusters in the Milky Way and other dwarf galaxies.

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arXiv2019

A tidal tale: detection of multiple stellar streams in the environment of NGC1052

The possible existence of two dark matter free galaxies (NGC1052-DF2 and NGC1052-DF4) in the field of the early-type galaxy NGC1052 presents a challenge to theories of dwarf galaxy formation according to the current cosmological paradigm. We carried out a search for signatures of past interactions connected to the putative hosts of NGC1052-DF2 and NGC1052-DF4 using a very deep L-band image obtained with the 0.7m Jeanne Rich telescope that reach a surface brightness limit of 28.5 mag arcsec-2 in the r band. We found several low-surface brightness features, possibly consistent with an ongoing merger history in this group. We find a tidal interaction between NGC1052 and NGC1047, confirming a physical association. Furthermore we find a stellar loop around NGC1052 in the direction of NGC1042 and a stellar stream pointing in the direction of NGC1052-DF2 - but both are not directly connected. We find no evidence for a recent tidal interaction for NGC1052-DF2 and NGC1052-DF4. No low surface brightness features have been uncovered around the spiral galaxy NGC1042, which leaves the association (physical or projected) between NGC1052 and NGC1042 ambiguous, though they have similar radial velocities. Their association will only be established once accurate distances to both objects have been measured.

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arXiv2019

A distance of 13 Mpc resolves the claimed anomalies of the galaxy lacking dark matter

The claimed detection of a diffuse galaxy lacking dark matter represents a possible challenge to our understanding of the properties of these galaxies and galaxy formation in general. The galaxy, already identified in photographic plates taken in the summer of 1976 at the UK 48-in Schmidt telescope, presents normal distance-independent properties (e.g. colour, velocity dispersion of its globular clusters). However, distance-dependent quantities are at odds with those of other similar galaxies, namely the luminosity function and sizes of its globular clusters, mass-to-light ratio and dark matter content. Here we carry out a careful analysis of all extant data and show that they consistently indicate a much shorter distance (13 Mpc) than previously indicated (20 Mpc). With this revised distance, the galaxy appears to be a rather ordinary low surface brightness galaxy (R_e=1.4+-0.1 kpc; M*=6.0+-3.6x10^7 Msun) with plenty of room for dark matter (the fraction of dark matter inside the half mass radius is >75% and M_halo/M*>20) corresponding to a minimum halo mass >10^9 Msun. At 13 Mpc, the luminosity and structural properties of the globular clusters around the object are the same as those found in other galaxies.

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