Jorge Sanchez Almeida

Instituto de Astrofísica de Canarias | IAC · Department of Astrophysics Research

This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of...

Tadpole galaxies, with a bright peripheral clump on a faint tail, are morphological types unusual in the nearby universe but very common early on. Low mass local tadpoles were identified and studied photometrically in a previous work, which we complete here analyzing their chemical and dynamical properties. We measure Halpha velocity curves of seve...

A systematic structuring of magnetic fields over scales much smaller than the mean free path of photospheric photons may be responsible for the observed asymmetrical Stokes profiles. We explore this possibility by deriving the radiative transfer equation for microstructured magnetic atmospheres (the MISMA approximation). This equation is subsequent...

We present a technique to model the instrumental polarization in the focal plane of a telescope. It takes into account that different rays of an incoming beam suffer different variation of the original polarization in their paths through the system. It also considers that the net effect depends on the way in which the different rays interfere with...

This paper is the second in a series that models photospheric magnetic structures in terms of atmospheres having optically thin fluctuations of magnetic field and thermodynamic state (the MISMA hypothesis). We apply an inversion procedure to the polarization of Fe I λ6301.5 and Fe I λ6302.5 observed in network and internetwork regions with the Adva...

Context. The halos of low-mass galaxies may allow us to constrain the nature of dark matter (DM), but the kinematic measurements needed to diagnose the required properties are technically extremely challenging. However, the photometry of these systems is doable. Aims. Using only stellar photometry, we wanted to constrain key properties of the DM ha...

*** Context: The halos of low-mass galaxies may allow us to constrain the nature of dark matter (DM), but the kinematic measurements to diagnose the required properties are technically extremely challenging. However, the photometry of these systems is doable. Aims. Using only stellar photometry, constrain key properties of the DM haloes in low-mass...

Unraveling the nature of dark matter (DM) stands as a primary objective in modern physics. Here we present evidence suggesting deviations from the collisionless Cold DM (CDM) paradigm. It arises from the radial distribution of stars in six Ultra Faint Dwarf (UFD) galaxies measured with the Hubble Space Telescope (HST). After a trivial renormalizati...

It was known that an ideal spherically symmetric stellar system with isotropic velocities and an inner core cannot reside in a Navarro, Frenk, and White (NFW) gravitational potential. The incompatibility can be pinned down to the radial gradient of the NFW potential in the very center of the system, which differs from zero. The gradient is identica...

It was known that an ideal spherically symmetric stellar system with isotropic velocities and an inner core cannot reside in a Navarro, Frenk, and White (NFW) gravitational potential. The incompatibility can be pinned down to the radial gradient of the NFW potential in the very center of the system, which differs from zero. The gradient is identica...

A long linear structure recently discovered could be the stellar wake produced by the passage of a runaway supermassive black hole (SMBH) or, alternatively, a bulgeless edge-on galaxy. We report on new very deep Hubble Space Telescope imaging that seems to be in tension with the SMBH runaway scenario but is consistent with the bulgeless edge-on gal...

A long linear structure recently discovered could be the stellar wake produced by the passage of a runaway supermassive black hole (SMBH) or, alternatively, a bulgeless edge-on galaxy. We report on new very deep HST imaging that seems to be in tension with the SMBH runaway scenario but is consistent with the bulgeless edge-on galaxy scenario. The n...

Context One of the most fundamental scaling relations in galaxies is observed between metallicity and stellar mass – the mass-metallicity relation (MZR) – although recently a stronger dependence of the gas-phase metallicity with the galactic gravitational potential (ΦZR) has been reported. Further dependences of metallicity on other galaxy properti...

Context. The usual approach to classify the ionizing source using optical spectroscopy is based on the use of diagnostic diagrams that compare the relative strength of pairs of collisitional metallic lines (e.g., [O III ] and [N II ]) to recombination hydrogen lines (e.g., H β and H α ). Despite it having been accepted as the standard procedure, it...

Context. Interpreting the scaling relations followed by galaxies is a fundamental tool for assessing how well we understand galaxy formation and evolution. Several scaling relations involving the galaxy metallicity have been discovered through the years, the foremost of which is the scaling with stellar mass. This so-called mass–metallicity relatio...

According to the current concordance cosmological model, dark matter (DM) particles are collisionless and produce self-gravitating structures with a central cusp, which, generally, is not observed. The observed density tends to a central plateau or core, explained within the cosmological model through the gravitational feedback of baryons on DM. Th...

Context. A recently discovered thin long object aligned with a nearby galaxy could be the stellar wake induced by the passage of a supermassive black hole (SMBH) kicked out from the nearby galaxy by the slingshot effect of a three-body encounter of SMBHs. Alternatively, the object could be a bulgeless edge-on galaxy coincidentally aligned with a se...

We present an application of unsupervised Machine Learning Clustering to the PAU Survey of galaxy spectral energy distribution (SED) within the COSMOS field. The clustering algorithm is implemented and optimized to get the relevant groups in the data SEDs. We find 12 groups from a total number of 5,234 targets in the survey at 0.01 < z <0.28. Among...

We present an application of unsupervised Machine Learning clustering to the PAU survey of galaxy spectral energy distribution (SED) within the COSMOS field. The clustering algorithm is implemented and optimized to get the relevant groups in the data SEDs. We find 12 groups from a total number of 5234 targets in the survey at 0.01 < z < 0.28. Among...

According to the current concordance cosmological model, the dark matter (DM) particles are collision-less and produce self-gravitating structures with a central cusp which, generally, is not observed. The observed density tends to a central plateau or core, explained within the cosmological model through the gravitational feedback of baryons on DM...

A recent paper 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 p...

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 o...

Nearby metal-poor starburst dwarf galaxies present a unique opportunity to probe the physics of high-density star formation with a detail and sensitivity unmatched by any observation of the high-z Universe. Here, we present the first results from a chemodynamical study of the nearby, gas-rich starburst dwarf CGCG 007-025. We use VLT/MUSE integral f...

Tadpole galaxies are metal-poor dwarfs with typically one dominant star-forming region, giving them a head–tail structure when inclined. A metallicity drop in the head suggests that gas accretion with even lower metallicity stimulated the star formation. Here we present multiband Hubble Space Telescope WFC3 and Advanced Camera for Surveys images of...

Nearby metal-poor starburst dwarf galaxies present a unique opportunity to probe the physics of high-density star formation with a detail and sensitivity unmatched by any observation of the high-z Universe. Here we present the first results from a chemodynamical study of the nearby, gas-rich starburst dwarf CGCG 007-025. We use VLT/MUSE integral fi...

Some dwarf galaxies are within the Mondian regime at all radii, i.e., the gravitational acceleration provided by the observed baryons is always below the threshold of g † ≃ 1.2 × 10 ⁻¹⁰ m s ⁻² . These dwarf galaxies often show cores, in the sense that, assuming Newton’s gravity to explain their rotation curves, the total density profile ρ ( r ) pre...

Tadpole galaxies are metal-poor dwarfs with typically one dominant star-forming region, giving them a head-tail structure when inclined. A metallicity drop in the head suggests that gas accretion with even lower metallicity stimulated the star formation. Here we present multiband HST WFC3 and ACS images of four nearby (<25 Mpc) tadpoles, SBS0, SBS1...

Some dwarf galaxies are within the Mondian regime at all radii, i.e., the gravitational acceleration provided by the observed baryons is always below the threshold of $g_\dag\simeq 1.2\times 10^{-10}\,{\rm m\,s^{-2}}$. These dwarf galaxies often show cores, in the sense that assuming Newton's gravity to explain their rotation curves, the total dens...

Aimed at the detection of cosmological gas being accreted onto galaxies in the local universe, we examined the H α emission in the halo of 164 galaxies in the field of view of the Multi-Unit Spectroscopic Explorer Wide survey (MUSE-Wide) with observable H α (redshift <0.42). An exhaustive screening of the corresponding H α images led us to select 1...

Aiming at the detection of cosmological gas being accreted onto galaxies of the local Universe, we examined the Halpha emission in the halo of 164 galaxies in the field of view of the Multi-Unit Spectroscopic Explorer Wide survey (\musew ) with observable Halpha (redshift < 0.42). An exhaustive screening of the corresponding Halpha images led us to...

Aimed at the detection of cosmological gas being accreted onto galaxies in the local universe, we examined the Hα emission in the halo of 164 galaxies in the field of view of the Multi-Unit Spectroscopic Explorer Wide survey (MUSE-Wide) with observable Hα (redshift <0.42). An exhaustive screening of the corresponding Hα images led us to select 118...

We do not have a final answer to the question of why galaxies choose a particular internal mass distribution. Here we examine whether the distribution is set by thermodynamic equilibrium (TE). Traditionally, TE is discarded for a number of reasons including the inefficiency of two-body collisions to thermalize the mass distribution in a Hubble time...

We do not have a final answer to the question of why galaxies choose a particular internal mass distribution. Here we examine whether the distribution is set by thermodynamic equilibrium (TE). Traditionally, TE is discarded for a number of reasons including the inefficiency of two-body collisions to thermalize the mass distribution in a Hubble time...

Polytropes have gained renewed interest because they account for several seemingly disconnected observational properties of galaxies. Here we study whether polytropes are also able to explain the stellar mass distribution within galaxies. We develop a code to fit surface density profiles using polytropes projected in the plane of the sky ( propol s...

We present a new measurement of the gas-phase mass–metallicity relation (MZR) and its dependence on star formation rates (SFRs) at 1.3 < z < 2.3. Our sample comprises 1056 galaxies with a mean redshift of z = 1.9, identified from the Hubble Space Telescope Wide Field Camera 3 (WFC3) grism spectroscopy in the Cosmic Assembly Near-infrared Deep Extra...

Polytropes have gained renewed interest because they account for several seemingly-disconnected observational properties of galaxies. Here we study if polytropes are also able to explain the stellar mass distribution within galaxies. We develop a code to fit surface density profiles using polytropes projected in the plane of the sky (propols). Sers...

We present a new measurement of the gas-phase mass-metallicity relation (MZR), and its dependence on star formation rates (SFRs) at 1.3 < z < 2.3. Our sample comprises 1056 galaxies with a mean redshift of z = 1.9, identified from the Hubble Space Telescope Wide Field Camera 3 (WFC3) grism spectroscopy in the Cosmic Assembly Near-Infrared Deep Extr...

Theory predicts that cosmological gas accretion plays a fundamental role fuelling star formation in galaxies. However, a detailed description of the accretion process to be used when interpreting observations is still lacking. Using the state-of-the-art cosmological hydrodynamical simulation eagle, we work out the chemical inhomogeneities arising i...

Theory predicts that cosmological gas accretion plays a fundamental role fuelling star formation in galaxies. However, a detailed description of the accretion process to be used when interpreting observations is still lacking. Using the state-of-the-art cosmological hydrodynamical simulation eagle, we work out the chemical inhomogeneities arising i...

Local star-forming galaxies show properties that are thought to differ from galaxies in the early Universe. Among them, the ionizing stellar populations and the gas geometry make the recipes designed to derive chemical abundances from nebular emission lines to differ from those calibrated in the Local Universe. A sample of 1969 extreme emission-lin...

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 appare...

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 appare...

Local star-forming galaxies show properties that are thought to differ from galaxies in the early Universe. Among them, the ionizing stellar populations and the gas geometry make the recipes designed to derive chemical abundances from nebular emission lines to differ from those calibrated in the Local Universe. A sample of 1969 Extreme Emission Lin...

While all models for the evolution of galaxies require the accretion of gas to sustain their growth via on-going star formation, it has proven difficult to directly detect this inflowing material. In this paper we use data of nearby star-forming galaxies in the SDSS IV Mapping Nearby Galaxies at Apache Point Observatory survey to search for evidenc...

While all models for the evolution of galaxies require the accretion of gas to sustain their growth via on-going star formation, it has proven difficult to directly detect this inflowing material. In this paper we use data of nearby star-forming galaxies in the SDSS IV Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey to search for...

The search for new global scaling relations linking the physical properties of galaxies has a fundamental interest. Furthermore, their recovery from spatially resolved relations has been in the spotlight of integral field spectroscopy (IFS). In this study, we investigate the existence of global and local relations between stellar age (Age ⋆ ) and g...

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 that show a central plateau or “core” in their density distribution. The proposed solutions to this core-cusp problem can be classified into two types. One invokes feedback mechanis...

The search for new global scaling relations linking physical properties of galaxies has a fundamental interest. Furthermore, their recovery from spatially resolved relations has been one of the spotlights of integral field spectroscopy (IFS). In this study we investigate the existence of global and local relations between stellar age ($Age_\star$)...

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...

MAAT is proposed as a visitor mirror-slicer optical system that will allow the OSIRIS spectrograph on the 10.4-m Gran telescopio CANARIAS (GTC) the capability to perform Integral Field Spectroscopy (IFS) over a seeing-limited FoV 14.20''x10'' with a slice width of 0.303''. MAAT@GTC will enhance the resolution power of OSIRIS by 1.6 times as compare...

The scatter in the galaxy size versus stellar mass (M⋆) relation gets largely reduced when, rather than the half-mass radius Re, the size at a fixed surface density is used. Here we address why this happens. We show how a reduction is to be expected because any two galaxies with the same M⋆ have at least one radius with identical surface density, w...

The scatter in the galaxy size versus stellar mass (Mstar) relation gets largely reduced when, rather than the half-mass radius Re, the size at a fixed surface density is used. Here we address why this happens. We show how a reduction is to be expected because any two galaxies with the same Mstar have at least one radius with identical surface dens...

Dark Matter (DM) is an ingredient essential to the current cosmological concordance model. It provides the gravitational pull needed for the baryons to form galaxies. Therefore, the existence of galaxies without DM is both disquieting and extremely interesting. Guo et al. recently presented "further evidence for a population of DM-deficient dwarf g...

The role of gas accretion in galaxy evolution is still a matter of debate. The presence of inflows of metal-poor gas that trigger star formation bursts of low metallicity has been proposed as an explanation for the local anticorrelation between star formation rate (SFR) and gas-phase metallicity ( Z g ) found in the literature. In the present study...

Context. The vast volume of data generated by modern astronomical surveys offers test beds for the application of machine-learning. In these exploratory applications, it is important to evaluate potential existing tools and determine those that are optimal for extracting scientific knowledge from the available observations. Aims. We explore the pos...

The vast volume of data generated by modern astronomical surveys offers test beds for the application of machine-learning. It is important to evaluate potential existing tools and determine those that are optimal for extracting scientific knowledge from the available observations. We explore the possibility of using clustering algorithms to separat...

We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analyzed spatially-resolved Hubble Space Telescope observations (imaging and slitless spectroscopy) of 53 star-forming galaxies at z ~ 1 - 3. We created continuum and emission line maps and pinpointed residual "blobs" detected after subtracting the galaxy disk....

We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analysed spatially resolved HubbleSpace Telescope observations (imaging and slitless spectroscopy) of 53 star-forming galaxies at z ∼ 1–3. We created continuum and emission line maps and pinpointed residual ‘blobs’ detected after subtracting the galaxy disc. Th...

The three-dimensional (3-D) shape of a galaxy inevitably is tied to how it has formed and evolved and to its dark matter halo. Local extremely metal-poor galaxies (XMPs; defined as having an average gas-phase metallicity < 0.1 solar) are important objects for understanding galaxy evolution largely because they appear to be caught in the act of accr...

[KKS2000]04 (NGC 1052-DF2) has become a controversial and well-studied galaxy after the claims suggesting a lack of dark matter and the presence of an anomalously bright globular cluster (GC) system around it. A precise determination of its overall star formation history (SFH) and a better characterization of its GC or planetary nebulae (PNe) syste...

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 (...

The fundamental metallicity relation (FMR) states that galaxies of the same stellar mass but larger star formation rate (SFR) tend to have smaller gas-phase metallicity ( ). It is thought to be fundamental because it naturally arises from the stochastic feeding of star formation from external metal-poor gas accretion, a process extremely elusive to...

The fundamental metallicity relation (FMR) states that galaxies of the same stellar mass but larger star formation rate (SFR) tend to have smaller gas-phase metallicity ( ). It is thought to be fundamental because it naturally arises from the stochastic feeding of star-formation from external metal-poor gas accretion, a process extremely elusive to...

The role of gas accretion in galaxy evolution is still a matter of debate. The presence of inflows of metal-poor gas that trigger star formation bursts of low metallicity has been proposed as an explanation for the local anti-correlation between star formation rate (SFR) and gas-phase metallicity ($\rm Z_g$) found in the literature. In the present...

[KKS2000]04 (NGC1052-DF2) has become a controversial and well-studied galaxy after the claims suggesting a lack of dark matter and the presence of an anomalously bright globular cluster (GC) system around it. A precise determination of its overall star formation history (SFH) as well as a better characterisation of its GC or planetary nebulae (PN)...

Correlations between the radio continuum, infrared, and CO emissions are known to exist for several types of galaxies and across several orders of magnitude. However, the low-mass, low-luminosity, and low-metallicity regime of these correlations is not well known. A sample of metal-rich and metal-poor dwarf galaxies from the literature has been ass...

We use data from 1222 late-type star-forming galaxies in the SDSS IV Mapping Nearby Galaxies at Apache Point Observatory survey to identify regions in which the gas-phase metallicity is anomalously low compared to expectations from the tight empirical relation between metallicity and stellar surface mass density at a given stellar mass. We find ano...

We use data from 1222 late-type star-forming galaxies in the SDSS IV MaNGA survey to identify regions in which the gas-phase metallicity is anomalously-low compared to expectations from the tight empirical relation between metallicity and stellar surface mass-density at a given stellar mass. We find anomalously low metallicity (ALM) gas in 10% of t...

The cosmological numerical simulations tell us that accretion of external metal-poor gas drives star formation (SF) in galaxy disks. One the best pieces of observational evidence supporting this prediction is the existence of low-metallicity star-forming regions in relatively high-metallicity host galaxies. The SF is thought to be fed by metal-poor...

Correlations between the radio continuum, infrared and CO emission are known to exist for several types of galaxies and across several orders of magnitude. However, the low-mass, low-luminosity and low-metallicity regime of these correlations is not well known. A sample of metal-rich and metal-poor dwarf galaxies from the literature has been assemb...

The cosmological numerical simulations tell us that accretion of external metal-poor gas drives star-formation (SF) in galaxy disks. One the best pieces of observational evidence supporting this prediction is the existence of low metallicity star-forming regions in relatively high metallicity host galaxies. The SF is thought to be fed by metal-poor...

We have serendipitously discovered that LeoncinoDwarf, an ultrafaint, low-metallicity recordholder dwarf galaxy, may have hosted a transient source, and possibly exhibited a change in morphology, a shift in the centre of brightness, and peak variability of the main (host) source in images taken approximately 40 yr apart; it is highly likely that th...

MEGARA is the new generation IFU and MOS optical spectrograph built for the 10.4m Gran Telescopio CANARIAS (GTC). The project was developed by a consortium led by UCM (Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain) and UPM (Spain). The instrument arrived to GTC on March 28 th 2017 and was successfully integrated and commissioned at the...

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 (...

A giant star-forming region in a metal-poor dwarf galaxy has been observed in optical lines with the 10 m Gran Telescopio Canarias (GTC) and in the emission line of CO(1-0) with the Northern Extended Millimeter Array (NOEMA) mm-wave interferometer. The metallicity was determined to be , from which we estimate a conversion factor of α CO ∼ 100 M o p...

For the same stellar mass, physically smaller star-forming galaxies are also metal richer. What causes the relation remains unclear. The central star-forming galaxies in the EAGLE cosmological numerical simulation reproduce the observed trend. We use them to explore the origin of the relation assuming that the physical mechanism responsible for the...