Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
126
result(s) for
"Espada, Daniel"
Sort by:
Galaxies in voids assemble their stars slowly
Galaxies in the Universe are distributed in a web-like structure characterized by different large-scale environments: dense clusters, elongated filaments, sheetlike walls and under-dense regions, called voids
1
–
5
. The low density in voids is expected to affect the properties of their galaxies. Indeed, previous studies
6
–
14
have shown that galaxies in voids are, on average, bluer and less massive, and have later morphologies and higher current star formation rates than galaxies in denser large-scale environments. However, it has never been observationally proved that the star formation histories (SFHs) in voids are substantially different from those in filaments, walls and clusters. Here we show that void galaxies have had, on average, slower SFHs than galaxies in denser large-scale environments. We also find two main SFH types present in all the environments: ‘short-timescale’ galaxies are not affected by their large-scale environment at early times but only later in their lives; ‘long-timescale’ galaxies have been continuously affected by their environment and stellar mass. Both types have evolved more slowly in voids than in filaments, walls and clusters.
We show that void galaxies have had slower star formation histories than galaxies in denser large-scale environments and find two main types of star formation history in all environments.
Journal Article
Investigating AGN/Starburst activities through ALMA multi-line observations in the mid-stage IR-bright merger VV 114
We present ALMA cycle 0 observations of the luminous merger VV 114. One of the main goals is to investigate mechanisms of molecular line ratio enhancement. Regions with the high 12CO (1–0)/13CO (1–0) and 12CO (3–2)/12CO (1–0) is located at a central filamentary structure (∼6 kpc) in VV 114. The filament consists of the eastern nucleus and the overlap region, where the galaxy disks are colliding. We also investigate these molecular line ratios on the Kennicutt-Schmidt law. VV 114 fills a gap between the “starburst” sequence and the “normal disk” sequence, and regions with the high ratios show the high ΣSFR and ΣH2. We suggest that the high ratios in VV 114 are due to star-forming activities in the both progenitor's nuclei and the merger-induced overlap region.
Journal Article
Investigating the evolution of merger remnants from the formation of gas disks
Our new compilation of interferometric CO data suggests that nuclear and extended molecular gas disks are common in the final stages of mergers. Comparing the sizes of the molecular gas disk and gas mass fractions to early-type and late-type galaxies, about half of the sample show similar properties to early-type galaxies, which have compact gas disks and low gas mass fractions. We also find that sources with extended gas disks and large gas mass fractions may become disk-dominated galaxies.
Journal Article
Identification of more than 40 gravitationally magnified stars in a galaxy at redshift 0.725
Strong gravitational magnification enables the detection of faint background sources and allows researchers to resolve their internal structures and even identify individual stars in distant galaxies. Highly magnified individual stars are useful in various applications, including studies of stellar populations in distant galaxies and constraining dark matter structures in the lensing plane. However, these applications have been hampered by the small number of individual stars observed, as typically one or a few stars are identified from each distant galaxy. Here, we report the discovery of more than 40 microlensed stars in a single galaxy behind Abell 370 at redshift of 0.725 (dubbed ‘the Dragon arc’) when the Universe was half of its current age, using James Webb Space Telescope observations with the time-domain technique. These events were found near the expected lensing critical curves, suggesting that these are magnified stars that appear as transients from intracluster stellar microlenses. Through multi-wavelength photometry, we constrained their stellar types and found that many of them are consistent with red giants or supergiants magnified by factors of hundreds. This finding reveals a high occurrence of microlensing events in the Dragon arc and demonstrates that time-domain observations by the James Webb Space Telescope could lead to the possibility of conducting statistical studies of high-redshift stars.
Using JWST, more than 40 individual stars have been detected in a distant galaxy, dating back to when the Universe was only half of its current age. The stars appear to be red (super)giants that are magnified by factors of hundreds.
Journal Article
JWST Discovery of $40+$ Microlensed Stars in a Magnified Galaxy, the \Dragon\ behind Abell 370
Strong gravitational magnification by massive galaxy clusters enable us to detect faint background sources, resolve their detailed internal structures, and in the most extreme cases identify and study individual stars in distant galaxies. Highly magnified individual stars allow for a wide range of applications, including studies of stellar populations in distant galaxies and constraining small-scale dark matter structures. However, these applications have been hampered by the small number of events observed, as typically one or a few stars are identified from each distant galaxy. Here, we report the discovery of 46 significant microlensed stars in a single strongly-lensed high-redshift galaxy behind the Abell 370 cluster at redshift of 0.725 when the Universe was half of its current age (dubbed the ``Dragon arc''), based on two observations separated by one year with the James Webb Space Telescope ({\\it JWST}). These events are mostly found near the expected lensing critical curves, suggesting that these are magnified individual stars that appear as transients from intracluster stellar microlenses. Through multi-wavelength photometry and colors, we constrain stellar types and find that many of them are consistent with red giants/supergiants magnified by factors of thousands. This finding reveals an unprecedented high occurrence of microlensing events in the Dragon arc, and proves that {\\it JWST}'s time-domain observations open up the possibility of conducting statistical studies of high-redshift stars and subgalactic scale perturbations in the lensing dark matter field.
Journal Article
Molecular Gas Excitation and Chemistry in VV 114 and NGC 1614 with ALMA
We present high resolution molecular line observations of dusty AGN and starburst in nearby luminous infrared galaxies (LIRGs), VV 114 (band 3/4/7) and NGC 1614 (band 3/6/7/9), with ALMA. Multi-frequency imaging from 4.8 GHz to 691 GHz of NGC 1614 allows us to study spatial properties of the radio-to-FIR continuum and multiple CO transitions, and we find the CO excitation up to J
upp = 6 can be explained by a single ISM model powered by nuclear starbursts. Our processing line imaging survey for VV 114 detected at least 30 molecular lines which show different chemical composition from region to region. Multi-molecule imaging helps us to diagnose the chemical differences of dusty ISM, while multi-transition imaging allows us to investigate gas physical conditions affected by nuclear activities directly.
Journal Article
ALMA Lensing Cluster Survey: Properties of Millimeter Galaxies Hosting X-ray Detected Active Galactic Nuclei
We report the multi-wavelength properties of millimeter galaxies hosting X-ray detected active galactic nuclei (AGNs) from the ALMA Lensing Cluster Survey (ALCS). ALCS is an extensive survey of well-studied lensing clusters with ALMA, covering an area of 133 arcmin\\(^2\\) over 33 clusters with a 1.2 mm flux-density limit of \\({\\sim}\\)60 \\(\\mathrm{\\mu Jy}\\) (\\(1\\sigma\\)). Utilizing the archival data of Chandra, we identify three AGNs at \\(z=\\)1.06, 2.09, and 2.84 among the 180 millimeter sources securely detected in the ALCS (of which 155 are inside the coverage of Chandra). The X-ray spectral analysis shows that two AGNs are not significantly absorbed (\\(\\log N_{\\mathrm{H}}/\\mathrm{cm}^{-2} < 23\\)), while the other shows signs of moderate absorption (\\(\\log N_{\\mathrm{H}}/\\mathrm{cm}^{-2}\\sim 23.5\\)). We also perform spectral energy distribution (SED) modelling of X-ray to millimeter photometry. We find that our X-ray AGN sample shows both high mass accretion rates (intrinsic 0.5--8 keV X-ray luminosities of \\({\\sim}10^{\\text{44--45}}\\,\\mathrm{erg\\ s^{-1}}\\)) and star-formation rates (\\({\\gtrsim}100\\,M_{\\odot}\\,\\mathrm{yr}^{-1}\\)). This demonstrates that a wide-area survey with ALMA and Chandra can selectively detect intense growth of both galaxies and supermassive black holes (SMBHs) in the high-redshift universe.
Paper
Morphological and Kinematical Analysis of the Double-barred Galaxy NGC 3504 Using ALMA CO (2-1) Data
We present results obtained from ALMA CO (2-1) data of the double-barred galaxy NGC 3504. With three times higher angular resolution (~ 0.\"8) than previous studies, our observations reveal an inner molecular gas bar, a nuclear ring, and four inner spiral arm-like structures in the central 1 kpc region. Furthermore, the CO emission is clearly aligned with the two dust lanes in the outer bar region, with differences in shape and intensity between them. The total molecular gas mass in the observed region (50\"x57\") is estimated to be \\(\\sim 3.1\\times 10^9 \\, {\\rm M}_{\\odot}\\), which is 17 per cent of the stellar mass. We used the Kinemetry package to fit the velocity field and found that circular motion strongly dominates at \\(R= 0.3-0.8\\) kpc, but radial motion becomes important at \\(R<0.3\\) kpc and \\(R=1.0-2.5\\) kpc, which is expected due to the presence of the inner and outer bars. Finally, assuming that the gas moves along the dust lanes in the bar rotating frame, we derived the pattern speed of the outer bar to be \\( 18\\pm5\\) km s\\(^{-1}\\) kpc\\(^{-1}\\), the average streaming velocities on each of the two dust lanes to be 165 and 221 km s\\(^{-1}\\), and the total mass inflow rate along the dust lanes to be 12 M\\(_{\\odot}\\) yr\\(^{-1}\\). Our results give a new example of an inner gas bar within a gas-rich double-barred galaxy and suggest that the formation of double-barred galaxies could be associated with the existence of such gas structures.
Paper
ALMA Lensing Cluster Survey: Dust mass measurements as a function of redshift, stellar-mass and star formation rate, from z=1 to z=5
Understanding the dust content of galaxies, its evolution with redshift and its relationship to stars and star formation is fundamental for our understanding of galaxy evolution. Using the ALMA Lensing Cluster Survey (ALCS) wide-area band-6 continuum dataset (\\(\\sim\\,\\)110 arcmin\\(^2\\) across 33 lensing clusters), we aimed at constraining the dust mass evolution with redshift, stellar mass and star formation rate (SFR). After binning sources according to redshift, SFR and stellar mass -- extracted from an HST-IRAC catalog -- we performed a set of continuum stacking analyses in the image domain using \\textsc{LineStacker} on sources between \\(z=1\\) and \\(z=5\\), further improving the depth of our data. The large field of view provided by the ALCS allows us to reach a final sample of \\(\\sim4000\\) galaxies with known coordinates and SED-derived physical parameters. We stack sources with SFR between \\(10^{-3}\\) and \\(10^{3}\\) M\\(_\\odot\\) per year, and stellar mass between \\(10^{8}\\) and \\(10^{12}\\) M\\(_\\odot\\), splitting them in different stellar mass and SFR bins. Through stacking we retrieve the continuum 1.2\\,mm flux, a known dust mass tracer, allowing us to derive the dust mass evolution with redshift and its relation with SFR and stellar mass. We observe clear continuum detections in the majority of the subsamples. From the non detections we derive 3-\\(\\sigma\\) upper limits. We observe a steady decline in the average dust mass with redshift. Moreover, sources with higher stellar mass or SFR have higher dust mass on average, allowing us to derive scaling relations. Our results are mostly in good agreement with models at \\(z\\sim1\\)-3, but indicate typically lower dust-mass than predicted at higher redshift.
Paper