Showing papers by "Enrichetta Iodice published in 2022"

Preparing for low surface brightness science with the Vera C. Rubin Observatory: characterisation of tidal features from mock images

Abstract: Tidal features in the outskirts of galaxies yield unique information about their past interactions and are a key prediction of the hierarchical structure formation paradigm. The Vera C. Rubin Observatory is poised to deliver deep observations for potentially of millions of objects with visible tidal features, but the inference of galaxy interaction histories from such features is not straightforward. Utilising automated techniques and human visual classification in conjunction with realistic mock images produced using the NewHorizon cosmological simulation, we investigate the nature, frequency and visibility of tidal features and debris across a range of environments and stellar masses. In our simulated sample, around 80 per cent of the flux in the tidal features around Milky Way or greater mass galaxies is detected at the 10-year depth of the Legacy Survey of Space and Time (30 − 31 mag arcsec−2), falling to 60 per cent assuming a shallower final depth of 29.5 mag arcsec−2. The fraction of total flux found in tidal features increases towards higher masses, rising to 10 per cent for the most massive objects in our sample (M⋆ ∼ 1011.5 M⊙). When observed at sufficient depth, such objects frequently exhibit many distinct tidal features with complex shapes. The interpretation and characterisation of such features varies significantly with image depth and object orientation, introducing significant biases in their classification. Assuming the data reduction pipeline is properly optimised, we expect the Rubin Observatory to be capable of recovering much of the flux found in the outskirts of Milky Way mass galaxies, even at intermediate redshifts (z < 0.2).

The Fornax Deep Survey with the VST. XII. Low surface brightness dwarf galaxies in the Fornax cluster

Abstract: Context. Low surface brightness (LSB) dwarf galaxies in galaxy clusters are an interesting group of objects as their contribution to the galaxy luminosity function and their evolutionary paths are not yet clear. Increasing the completeness of our galaxy catalogs is crucial for understanding these galaxies, which have e ff ective surface brightnesses below 23magarcsec − 2 (in optical). Progress is continuously being made via the performance of deep observations, but detection depth and the quantification of the completeness can also be improved via the application of novel approaches in object detection. For example, the Fornax subgroup of large LSB so-called ultra-di ff use galaxies.

The Fornax3D project: discovery of ancient massive merger events in the Fornax cluster galaxies NGC 1380 and NGC 1427

Abstract: We report the discovery of ancient massive merger events in the early-type galaxies NGC1380 and NGC1427 in the Fornax galaxy cluster. Both galaxies are observed by the MUSE IFU instrument on the VLT, as part of the Fornax3D project. By fitting recently-developed population-orbital superposition models to the observed surface brightness as well as stellar kinematic, age, and metallicity maps, we obtain the stellar orbits, age and metallicity distributions of each galaxy. We then decompose each galaxy into multiple orbital-based components, including a dynamically hot inner stellar halo component which is identified as the relic of past massive mergers. By comparing to analogues from cosmological galaxy simulations, chiefly TNG50, we find that the formation of such a hot inner stellar halo requires the merger with a now-destroyed massive satellite galaxy of 3 . 7 + 2 . 7 − 1 . 5 × 10 10 M (cid:12) (about 1 / 5 of its current stellar mass) and of 1 . 5 + 1 . 6 − 0 . 7 × 10 10 M (cid:12) (about 1 / 4 of its current stellar mass) in the case of NGC1380 and NGC1427, respectively. Moreover, we infer that the last massive merger in NGC1380 happened ∼ 10 Gyr ago based on the stellar age distribution of the re-grown dynamically cold disk, whereas the merger in NGC1427 ended t (cid:46) 8 Gyr ago based on the stellar populations in its hot inner stellar halo. The major merger event in NGC1380 is the first one with both merger mass and merger time quantitatively inferred in a galaxy beyond the Local Volume. Moreover, it is the oldest and most massive one uncovered in nearby galaxies so far.

Galaxy populations in the Hydra I cluster from the VEGAS survey. II. The ultra-diffuse galaxy population

Abstract: In this work, we extend the catalog of low-surface brightness (LSB) galaxies, including ultra-di ff use galaxy (UDG) candidates, within ≈ 0 . 4 R vir of the HydraI cluster of galaxies based on deep images from the VST Early-type GAlaxy Survey (VEGAS). The new galaxies were found by applying an automatic detection tool and carrying out additional visual inspections of g and r band images. This led to the detection of 11 UDGs and 8 more LSB galaxies. For all of them, we assessed the cluster membership using the color– magnitude relation derived for early-type giant and dwarf galaxies in HydraI. The UDGs and new LSB galaxies found in Hydra I span a wide range of central surface brightness (22 . 7 (cid:46) µ 0 ,g (cid:46) 26 . 5magarcsec − 2 ), e ff ective radius (0 . 6 (cid:46) R e (cid:46) 4 . 0kpc), and color (0 . 4 ≤ g − r ≤ 0 . 9mag), and have stellar masses in the range ∼ 5 × 10 6 − 2 × 10 8 M (cid:12) . The 2D projected distribution of both galaxy types is similar to the spatial distribution of dwarf galaxies, with over-densities in the cluster core and north of the cluster center. They have similar color distribution and comparable stellar masses to the red dwarf galaxies. Based on photometric selection, we identify a total of nine globular cluster (GC) candidates associated to the UDGs and four to the LSB galaxies, with the highest number of candidates in an individual UDG being three. We find that there are no relevant di ff erences between dwarfs, LSB galaxies, and UDGs: the structural parameters (i.e., surface brightness, size, color, and n -index) and GC content of the three classes have similar properties and trends. This finding is consistent with UDGs being the extreme LSB tail of the size–luminosity distribution of dwarfs in this environment.

The Intra-Group Baryons in the LEO I Pair From the VST Early-Type GAlaxy Survey

Abstract: In this paper we present the deep, wide-field and multi-band imaging of the LEO I pair NGC 3379-NGC 3384, from the VST Early-type GAlaxy Survey (VEGAS). The main goal of this study is to map the intra-group baryons in the pair, in the form of diffuse light and globular clusters (GCs). Taking advantage from the large covered area, which extends for ∼ 3.9 square degrees around the pair, and the long integration time, we can map the light distribution out to ∼ 63 kpc and down to ∼ 30 mag/arcsec2 in the g band and ∼ 29 mag/arcsec2 in the r band, deeper than previous data available for this target. The map of the intra-group light (IGL) presents two very faint (μ g ∼ 28-29 mag/arcsec2) streams protruding from the brightest group member NGC 3379 and elongated toward North-West and South. We estimate that the fraction of the stellar halo around NGC 3379 plus the intra-group light is ∼ 17 ± 2 % in both g and r bands, with an average color g-r = 0.75 ± 0.04 mag. The color distribution of the GCs appears multi-modal, with two dominant peaks at (u-r) = 1.8 mag and (u-r) = 2.1 mag, respectively. The GC population stretches from North-East to South-West and from North-West to South of the pair, in the last case overlapping with the streams of IGL, as well as the PNe distribution found by Hartke et al. (Hartke et al., A&A, 2020, 642, A46) and Hartke et al. (Hartke et al., 2022). Since these structures are elongated in the direction of the two nearby galaxies M96 and NGC 3338, they could be the remnant of a past gravitational interactions with the pair.

The Fornax3D project: The environmental impact on gas metallicity gradients in Fornax cluster galaxies

Abstract: The role played by environment in galaxy evolution is a topic of ongoing debate among astronomers. There has been little success in elucidating the degree to which environment can alter, re-shape, or drive galaxy evolution, that is, using either observations or simulations. However, our knowledge of the effect of environment on gas metallicity gradients remains limited. Here we present our analysis of the gas metallicity gradients for a sample of ten Fornax cluster galaxies observed with MUSE as part of the Fornax3D project. We used detailed maps of emission lines to determine precise values of gas metallicity and metallicity gradients. The integrated gas metallicity of our Fornax cluster galaxies shows slightly higher metallicities (∼0.045 dex) in comparison to a control sample. In addition, we find signs of a mass and metallicity segregation from the center to the outskirts of the cluster. By comparing our Fornax cluster metallicity gradients with a control sample we find a general median offset of ∼0.04 dex/Re, with eight of our galaxies showing flatter or more positive gradients. The intermediate infallers in our Fornax sample show more positive gradients with respect to the control sample. We find no systematic difference between the gradients of recent and intermediate infallers when considering the projected distance of each galaxy to the cluster center. To identify the origin of the observed offset in the metallicity gradients, we performed a similar analysis with data from the TNG50 simulation. We identify 12 subhalos in Fornax-like clusters and compared their metallicity gradients with a control sample of field subhalos. This exercise also shows a flattening in the metallicity gradients for galaxies in Fornax-like halos, with a median offset of ∼0.05 dex/Re. We also analyzed the merger history, Mach numbers (M), and ram pressure stripping of our TNG50 sample. We conclude that the observed flattening in metallicity gradients is likely due to a combination of galaxies traveling at supersonic velocities (M > 1), which are experiencing high ram pressure stripping and flybys.

Fornax3D project: Assembly history of massive early-type galaxies in the Fornax cluster from deep imaging and integral field spectroscopy

Abstract: This work is based on high-quality integral-field spectroscopic data obtained with the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT). The 21 brightest ( m B ≤ 15mag) early-type galaxies (ETGs) inside the virial radius of the Fornax cluster are observed out to distances of ∼ 2 − 3 R e . Deep imaging from the VLT Survey Telescope (VST) is also available for the sample ETGs. We investigated the variation of the galaxy structural properties as a function of the total stellar mass and cluster environment. Moreover, we correlated the size scales of the luminous components derived from a multi-component decomposition of the VST surface-brightness radial profiles of the sample ETGs with the MUSE radial profiles of stellar kinematic and population properties. The results are compared with both theoretical predictions and previous observational studies and used to address the assembly history of the massive ETGs of the Fornax cluster. We find that galaxies in the core and north-south clump of the cluster, which have the highest accreted mass fraction, show milder metallicity gradients in their outskirts than the galaxies infalling into the cluster. We also find a segregation in both age and metallicity between the galaxies belonging to the core and north-south clump and the infalling galaxies. The new findings fit well within the general framework for the assembly history of the Fornax cluster.

The cycle of metals in the infalling elliptical galaxy NGC 1404

Abstract: Hot atmospheres pervading galaxy clusters, groups, and early-type galaxies are rich in metals, produced during epochs and diffused via processes that are still to be determined. While this enrichment has been routinely investigated in clusters, metals in lower mass systems are more challenging to probe with standard X-ray exposures and spectroscopy. In this paper, we focus on very deep XMM-Newton (∼350 ks) observations of NGC1404, a massive elliptical galaxy experiencing ram-pressure stripping of its hot atmosphere while infalling towards the centre of the Fornax cluster, with the aim to derive abundances through its hot gas extent. Importantly, we report the existence of a new fitting bias – the “double Fe bias” – leading to an underestimate of the Fe abundance when two thermal components cannot realistically model the complex temperature structure present in the outer atmosphere of the galaxy. Contrasting with the “metal conundrum” seen in clusters, the Fe and Mg masses of NGC1404 are measured 1–2 orders of magnitude below what stars and supernovae could have reasonably produced and released. In addition, we note the remarkable Solar abundance ratios of the galaxy’s halo, different from its stellar counterpart but similar to the chemical composition of the ICM of rich clusters. Completing the clusters regime, all these findings provide additional support towards a scenario of early enrichment, at play over two orders of magnitude in mass. A few peculiar and intriguing features, such as a possible double metal peak as well as an apparent ring of enhanced Si near the galaxy core, are also discussed.

A slow bar in the lenticular barred galaxy NGC 4277

Abstract: Aims. We characterised the properties of the bar hosted in lenticular galaxy NGC4277, which is located behind the Virgo cluster. Methods. We measured the bar length and strength from the surface photometry obtained from the broad-band imaging of the Sloan Digital Sky Survey and we derived the bar pattern speed from the stellar kinematics obtained from the integral-field spectroscopy performed with the Multi Unit Spectroscopic Explorer at the Very Large Telescope. We also estimated the co-rotation radius from the circular velocity, which we constrained by correcting the stellar streaming motions for asymmetric drift, and we finally derived the bar rotation rate. Results. We found that NGC4277 hosts a short ( R bar = 3 . 2 + 0 . 9 − 0 . 6 kpc), weak ( S bar = 0 . 21 ± 0 . 02), and slow ( R = 1 . 8 + 0 . 5 − 0 . 3 ) bar and its pattern speed ( Ω bar = 24 . 7 ± 3 . 4 km s − 1 kpc − 1 ) is amongst the best-constrained ones ever obtained with the Tremaine-Weinberg (TW) method with relative statistical errors of ∼ 0 . 2. Conclusions. NGC4277 is the first clear-cut case of a galaxy hosting a slow stellar bar ( R > 1 . 4 at more than a 1 σ confidence level) measured with the model-independent TW method. A possible interaction with the neighbour galaxy NGC4273 could have triggered the formation of such a slow bar and / or the bar could be slowed down due to the dynamical friction with a significant amount of dark matter within the bar region.

The Fornax3D Project: Intrinsic Correlations between orbital properties and the stellar Initial Mass Function

Abstract: Variations of the stellar Initial Mass Function (IMF) in external galaxies have been inferred from a variety of independent probes. Yet the physical conditions causing these variations remain largely unknown. In this work, we explore new spatially-resolved measurements of the IMF for three edge-on lenticular galaxies in the Fornax cluster. We utilize existing orbit-based dynamical models in order to fit the new IMF maps within an orbital framework. We find that, within each galaxy, the high-angular-momentum, disk-like stars exhibit an IMF which is rich in dwarf stars. The centrally-concentrated pressure-supported orbits exhibit similarly dwarf-rich IMF. Conversely, orbits at large radius which have intermediate angular momentum exhibit IMF which are markedly less dwarf-rich relative to the other regions of the same galaxy. Assuming that the stars which reside, in the present-day, on dynamically-hot orbits at large radii are dominated by accreted populations, we interpret these findings as a correlation between the dwarf-richness of a population of stars, and the mass of the host in which it formed. Specifically, deeper gravitational potentials would produce more dwarf-rich populations, resulting in the relative deficiency of dwarf stars which originated in the lower-mass accreted satellites. The central and high angular-momentum populations are likely dominated by in-situ stars, which were formed in the more massive host itself. There are also global differences between the three galaxies studied here, of up to ∼0.3 dex in the IMF parameter ξ. We find no local dynamical or chemical property which alone can fully account for the IMF variations.

Does the virial mass drive the intra-cluster light? Relationship between the ICL and Mvir from VEGAS

Abstract: In this Letter we revisit the relationship between the fraction of the intra-cluster light (ICL) and both the virial mass and the fraction of Early Type Galaxies in the host halo. This is based on a statistically significant and homogeneous sample of 22 groups and clusters of galaxies in the local Universe ($z \leq 0.05$), obtained with the VST Early-type GAlaxy Survey (VEGAS). Taking advantage of the long integration time and large area of the VEGAS images, we are able to map the galaxy outskirts and ICL down to $\mu_g$ $\geq$ 29-30 mag/arcsec$^2$ and out to hundreds of kpc. With this data-set, we have expanded the sample of ICL measurements, doubling the previous measures available from the literature for z $\leq$ 0.05. The main result of this work is the lack of any significant trend between the fraction of ICL and the virial mass of the host environment, covering a wide range of virial masses ( $\sim$ $10^{12.5} \leq M_{vir} \leq 10^{15.5} M_{\odot}$), in agreement with some theoretical studies. Since the new data points are all derived with the same methodology and from the same observational setup, and all have comparable depth, the large observed scatter indicates an intrinsic variation in the ICL fraction.On the other hand, there is a weak relation between the fraction of ICL and the fraction of Early Type Galaxies in the host halo, where a larger fraction of ICL is found in groups and clusters of galaxies dominated by earlier morphological types, indicating a connection between the ICL and the dynamical state of the host system.

Properties of intra-cluster low-mass X-ray binaries in Fornax globular clusters

Abstract: Aims. We present a study of the intra-cluster population of low-mass X-ray binaries (LMXB) residing in globular clusters (GC) in the central 1deg 2 of the Fornax galaxy cluster. Di ff erently from previous studies, which were restricted to the innermost regions of individual galaxies, this work is aimed at comparing the properties of the intra-cluster population of GC-LMXBs with those of the host galaxy. The this a of the VLT Survey Telescope We performed a cross-match between the optical and the X-ray catalogue in order to identify the LMXBs in GCs. We the GC-LMXBs host-galaxy and intra-cluster on their distance in of e ff ective ( R e GC-LMXBs also depends on GC colour, we Gaussian mixture model to into red and blue GCs. spectral properties of LMXBs and the host GC colour and therefore its metallicity. We discuss the possibilities of spatial biases due to uncertainties in the X-ray spectral response correction and due to contamination by background active galactic nuclei.

The SAMI -- Fornax Dwarfs Survey II: The Stellar Mass Fundamental Plane and the Dark Matter fraction of Dwarf Galaxies

Abstract: We explore the kinematic scaling relations of 38 dwarf galaxies in the Fornax Cluster using observations from the SAMI integral field spectrograph. We focus on the Fundamental Plane (FP), defined by the physical properties of the objects (scale length, surface brightness and velocity dispersion) and the Stellar Mass (Fundamental) Plane, where surface brightness is replaced by stellar mass, and investigate their dynamical-to-stellar-mass ratio. We confirm earlier results that the Fornax dEs are significantly offset above the FP defined by massive, hot stellar systems. For the Stellar Mass (Fundamental) Plane, which shows much lower scatter, we find that young and old dwarf galaxies lie at about the same distance from the plane, all with comparable scatter. We introduce the perpendicular deviation of dwarf galaxies from the Stellar Mass Plane defined by giant early-types as a robust estimate of their DM fraction, and find that the faintest dwarfs are systematically offset above the plane, implying that they have a higher dark matter fraction. This result is confirmed when estimating the dynamical mass of our dEs using a virial mass estimator, tracing the onset of dark matter domination in low mass stellar systems. We find that the position of our galaxies on the Stellar Mass FP agrees with the galaxies in the Local Group. This seems to imply that the processes determining the position of dwarf galaxies on the FP depend on the environment in the same way, whether the galaxy is situated in the Local Group or in the Fornax Cluster.

Dorado and its member galaxies III. Mapping star formation with FUV imaging from UVIT (cid:63)

Abstract: Context. We are investigating the star formation in galaxies of the actively evolving Dorado group where, for a large fraction of both early- and late-type galaxies, signatures of interactions and merging events are revealed by optical and radio observations. Aims. Our previous H α + [N II] study, probing ≈ 10Myr timescales, suggested that star formation is still ongoing in early-type galaxies. In this work, we use far-UV (FUV) imaging to map recent star formation on longer timescales, on the order of 100Myr. Methods. We used the Ultraviolet Imaging Telescope UVIT on board Astrosat to image the galaxies of the Dorado backbone previously observed in H α + [N II], timescales.

Dorado group of galaxies.III. Mapping star formation with FUV imaging from UVIT

Abstract: Context. We are investigating the star formation in galaxies of the actively evolving Dorado group where, for a large fraction of both early- and late-type galaxies, signatures of interactions and merging events are revealed by optical and radio observations. Aims. Our previous H α + [N II] study, probing ≈ 10 Myrs timescales, suggested that star formation is still ongoing in early-type galaxies. In this work, we use far-UV (FUV) imaging to map recent star formation on longer times scales, of the order of 100 Myrs. Methods. We used the Ultraviolet telescope UVIT on board Astrosat to image the galaxies of the Dorado backbone previously observed in H α + [N II] , with the far-UV filter FUV.CaF2 (1300-1800 Å). The sample includes NGC 1536, NGC 1546, NGC 1549, [CMI2001]4136-01, NGC 1553, IC 2058, PGC 75125,NGC 1566, NGC 1596 and NGC 1602; for the two latter galaxies, the UVIT data provide the first view in far-UV. For the others, previously observed by GALEX, the UVIT data a ff ord a ∼ 5 × improvement in spatial resolution. Results. FUV.CaF2 emission is revealed in all the Dorado galaxies observed, tracing young stellar populations in ring structures and showing tidal distortions. The Sérsic index, derived by fitting the luminosity profiles, is always n < 3 suggesting that the FUV.CaF2 emission originates from a disk also in early-type galaxies. The star formation rate (SFR) ranges from 0.004 ± 0.001 M (cid:12) yr − 1 of [CMI2001]4136-01 to 2.455 ± 0.027 M (cid:12) yr − 1 of NGC 1566. Most of the recent star formation is found at the periphery of the Dorado group where most of late-type galaxies are located. For these galaxies, the ratio SFR H α / SFR FUV . CaF 2 is close to 1, except for the edge- on IC 2058, similarly to previously reported relations for Local Volume samples. For early-type galaxies, however, SFR H α is about 15 times higher than SFR FUV . The Dorado’s early-type galaxies define a separate locus in SFR FUV , SFR H α space with respect to the late-type galaxies, which is well represented by the relation log (SFR FUV . CaF 2 ) = 0.70 × log (SFR H α ) − 1 . 26. Conclusions. The disk structure of the FUV.CaF2 emitting populations discovered in all the early-types galaxies implies dissipa- tive processes and wet merging events. The systematic discrepancy between SFRs derived from H α and FUV fluxes suggests that rejuvenation episodes in early-type galaxies cannot sustain constant star formation over ∼ 100 Myrs timescales.