14 research outputs found
Unveiling the outskirts of galaxies using deep imaging.
La forma habitual de medir el tamaño de las galaxias, el radio efectivo, es el resultado de una época cuando las imágenes astronómicas eran poco profundas y, por tanto, incapaces de capturar la extensión completa de las fuentes astronómicas. Esta situación ha cambiado drásticamente en la actualidad con la llegada de cartografiados muy profundos. Estas nuevas imágenes nos han permitido estudiar las características de las galaxias en sus regiones externas y débiles, permitiéndonos explorar críticamente nuestras convenciones sobre el tamaño de estos objetos. Por este motivo, ha llegado el momento de sustituir una definición de tamaño basado en la concentración de la luz, el radio efectivo, por una definición que capture el concepto intuitivo de tamaño de las galaxias, como su borde o frontera. En este trabajo, proponemos una nueva definición de tamaño de las galaxias basada en la posición del umbral de la densidad de gas necesario para formar estrellas. Esta es una definición de tamaño con motivación física. Es importante resaltar que esta nueva definición de tamaño no sólo captura lo que la visión humana identifica como borde de la galaxia, sino que además reduce de forma drástica la dispersión de la relación masa-tamaño en un factor mayor que dos. Comparada con otras definiciones de tamaño, la nueva forma de medir la extensión de las galaxias es única, en el sentido que unifica en una única relación masa-tamaño, galaxias que difieren hasta cinco ordenes de magnitud en masa. Para poner nuestros resultados en el contexto de la formación y evolución de galaxias, exploramos como cambia nuestro entendimiento del origen de las galaxias discos y la naturaleza de las galaxias ultra-difusas
The edges of galaxies in the Fornax Cluster: Fifty percent smaller and denser compared to the field
Physically motivated measurements are crucial for understanding galaxy growth
and the role of the environment on their evolution. In particular, the growth
of galaxies as measured by their size or radial extent provides an empirical
approach for addressing this issue. However, the established definitions of
galaxy size used for nearly a century are ill-suited for these studies because
of a previously ignored bias. The conventionally-measured radii consistently
miss the diffuse, outer extensions of stellar emission which harbour key
signatures of galaxy growth, including star formation and gas accretion or
removal. This issue is addressed by examining low surface brightness
truncations or galaxy "edges" as a physically motivated tracer of size based on
star formation thresholds. Our total sample consists of galaxies with
stellar masses ranging from .
This sample of nearby cluster, group satellite and nearly isolated field
galaxies was compiled using multi-band imaging from the Fornax Deep Survey,
deep IAC Stripe 82 and Dark Energy Camera Legacy Surveys. Across the full mass
range studied, we find that compared to the field, the edges of galaxies in the
Fornax Cluster are located at 50% smaller radii and the average stellar surface
density at the edges are two times higher. These results are consistent with
the rapid removal of loosely bound neutral hydrogen (HI) in hot, crowded
environments which truncates galaxies outside-in earlier, preventing the
formation of more extended sizes and lower density edges. In fact, we find that
galaxies with lower HI fractions have edges with higher stellar surface
density. Our results highlight the importance of deep imaging surveys to study
the low surface brightness imprints of the large scale structure and
environment on galaxy evolution.Comment: 22 pages, 12 figures, 2 tables, submitted to A&A after LSST DESC
internal and collaboration wide review (see acknowledgements). Example
galaxies in Figs. 2, 5 and 6. Key results in Figs. 7, 8, 11 and 1
An almost dark galaxy with the mass of the Small Magellanic Cloud
Almost Dark Galaxies are objects that have eluded detection by traditional
surveys such as the Sloan Digital Sky Survey (SDSS). The low surface brightness
of these galaxies ((0) mag/arcsec^2), and hence their low surface
stellar mass density (a few solar masses per pc^2 or less), suggests that the
energy density released by baryonic feedback mechanisms is inefficient in
modifying the distribution of the dark matter halos they inhabit. For this
reason, almost dark galaxies are particularly promising for probing the
microphysical nature of dark matter. In this paper, we present the
serendipitous discovery of Nube, an almost dark galaxy with e~ 26.7
mag/arcsec^2. The galaxy was identified using deep optical imaging from the IAC
Stripe82 Legacy Project. Follow-up observations with the 100m Green Bank
Telescope strongly suggest that the galaxy is at a distance of 107 Mpc.
Ultra-deep multi-band observations with the 10.4m Gran Telescopio Canarias
favour an age of ~10 Gyr and a metallicity of [Fe/H]. With a stellar
mass of ~4x10^8 Msun and a half-mass radius of Re=6.9 kpc (corresponding to an
effective surface density of ~0.9 Msun/pc^2), Nube is the most massive and
extended object of its kind discovered so far. The galaxy is ten times fainter
and has an effective radius three times larger than typical ultra-diffuse
galaxies with similar stellar masses. Galaxies with comparable effective
surface brightness within the Local Group have very low mass (~10^5 Msun) and
compact structures (effective radius Re<1 kpc). Current cosmological
simulations within the cold dark matter scenario, including baryonic feedback,
do not reproduce the structural properties of Nube. However, its highly
extended and flattened structure is consistent with a scenario where the dark
matter particles are ultra-light axions with a mass of
m=() eV.}Comment: Accepted for publication in A&A. Main figures are 8, 9 and 1
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 2 × 8.4 m Large Binocular Telescope (LBT) aiming to explore the stellar haloes and the low surface brightness population of satellites down to a depth of μV ∼31 mag arcsec-2 (3σ in 10″ × 10″ boxes) of nearby galaxies. We simultaneously collected deep imaging in the g and r Sloan filters using the Large Binocular Cameras. The resulting images are 60 times (i.e. ∼4.5 mag) deeper than those from the Sloan Digital Sky Survey, 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 NGC 1042 (an M 33 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 ± 0.4 × 108 M) is in agreement with the ΛCDM expectations. Additionally, we show that deep imaging from the LBT reveals low mass satellites (a few times 105 M) with very faint central surface brightness μV(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. © 2021 ESO.We acknowledge support from grant PID2019-107427GB-C32 from The Spanish Ministry of Science and Innovation. We acknowledge financial support from the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement No 721463 to the SUNDIAL ITN network, and the European Regional Development Fund (FEDER), from IAC project P/300624, financed by the Ministry of Science, Innovation and Universities, through the State Budget and by the Canary Islands Department of Economy, Knowledge and Employment, through the Regional Budget of the Autonomous Community. DZ acknowledges financial support from NSF AST-2006785. NC acknowledges support from the research project grant "Understanding the Dynamic Universe" funded by the Knut and Alice Wallenberg Foundation under Dnr KAW 2018.0067 and Chris Usher for interesting comments. DJS acknowledges support from NSF grants AST-1821967 and 1813708. JR acknowledges funding from the State Agency for Research of the Spanish MCIU through the `Center of Excellence Severo Ochoa' award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709), financial support from the grants AYA2015-65973-C3-1-R and RTI2018-096228B-C31 (MINECO/FEDER, UE) as well as support from the State Research Agency (AEI-MCINN) of the Spanish Ministry of Science and Innovation under the grant `The structure and evolution of galaxies and their central regions' with reference PID2019-105602GB-I00/10.13039/501100011033. The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona Board of Regents; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, The Leibniz Institute for Astrophysics Potsdam, and Heidelberg University; The Ohio State University, representing OSU, University of Notre Dame, University of Minnesota and University of Virginia. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. This work was partly done using GNU Astronomy Utilities (Gnuastro, ascl.net/1801.009) version 0.13.12-f50c. Work on Gnuastro has been funded by the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT) scholarship and its Grant-in-Aid for Scientific Research (21244012, 24253003), the European Research Council (ERC) advanced grant 339659-MUSICOS, and the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number AYA2016-76219-P.Peer reviewe
Extragalactic Star Cluster Science with the Nancy Grace Roman Space Telescope's High Latitude Wide Area Survey and the Vera C. Rubin Observatory
The Nancy Grace Roman Telescope's High Latitude Wide Area Survey will have a
number of synergies with the Vera Rubin Observatory's Legacy Survey of Space
and Time (LSST), particularly for extragalactic star clusters. Understanding
the nature of star clusters and star cluster systems are key topics in many
areas of astronomy, chief among them stellar evolution, high energy
astrophysics, galaxy assembly/dark matter, the extragalactic distance scale,
and cosmology. One of the challenges will be disentangling the age/metallicity
degeneracy because young (Myr) metal-rich clusters have similar SEDs to
old (Gyr) metal-poor clusters. Rubin will provide homogeneous,
photometric coverage, and measurements in the red Roman filters will help break
the age-metallicity and age-extinction degeneracies, providing the first
globular cluster samples that cover wide areas while essentially free of
contamination from Milky Way stars. Roman's excellent spatial resolution will
also allow measurements of cluster sizes. We advocate for observations of a
large sample of galaxies with a range of properties and morphologies in the
Rubin/LSST footprint matching the depth of the LSST Wide-Fast-Deep field
band limit (26.3 mag), and recommend adding the F213 filter to the survey.Comment: white paper submitted for Roman CCS inpu
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 our 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
Optimising and comparing source-extraction tools using objective segmentation quality criteria
Abstract
Context.: With the growth of the scale, depth, and resolution of astronomical imaging surveys, there is increased need for highly accurate automated detection and extraction of astronomical sources from images. This also means there is a need for objective quality criteria, and automated methods to optimise parameter settings for these software tools.
Aims: We present a comparison of several tools developed to perform this task: namely SExtractor, ProFound, NoiseChisel, and MTObjects. In particular, we focus on evaluating performance in situations that present challenges for detection. For example, faint and diffuse galaxies; extended structures, such as streams; and objects close to bright sources. Furthermore, we develop an automated method to optimise the parameters for the above tools.
Methods: We present four different objective segmentation quality measures, based on precision, recall, and a new measure for the correctly identified area of sources. Bayesian optimisation is used to find optimal parameter settings for each of the four tools when applied to simulated data, for which a ground truth is known. After training, the tools are tested on similar simulated data in order to provide a performance baseline. We then qualitatively assess tool performance on real astronomical images from two different surveys.
Results: We determine that when area is disregarded, all four tools are capable of broadly similar levels of detection completeness, while only NoiseChisel and MTObjects are capable of locating the faint outskirts of objects. MTObjects achieves the highest scores on all tests for all four quality measures, whilst SExtractor obtains the highest speeds. No tool has sufficient speed and accuracy to be well suited to large-scale automated segmentation in its current form
Snowmass2021: Vera C. Rubin Observatory as a Flagship Dark Matter Experiment
Establishing that Vera C. Rubin Observatory is a flagship dark matter experiment is an essential pathway toward understanding the physical nature of dark matter. In the past two decades, wide-field astronomical surveys and terrestrial laboratories have jointly created a phase transition in the ecosystem of dark matter models and probes. Going forward, any robust understanding of dark matter requires astronomical observations, which still provide the only empirical evidence for dark matter to date. We have a unique opportunity right now to create a dark matter experiment with Rubin Observatory Legacy Survey of Space and Time (LSST). This experiment will be a coordinated effort to perform dark matter research, and provide a large collaborative team of scientists with the necessary organizational and funding supports. This approach leverages existing investments in Rubin. Studies of dark matter with Rubin LSST will also guide the design of, and confirm the results from, other dark matter experiments. Supporting a collaborative team to carry out a dark matter experiment with Rubin LSST is the key to achieving the dark matter science goals that have already been identified as high priority by the high-energy physics and astronomy communities
Snowmass2021: Vera C. Rubin Observatory as a Flagship Dark Matter Experiment
Establishing that Vera C. Rubin Observatory is a flagship dark matter experiment is an essential pathway toward understanding the physical nature of dark matter. In the past two decades, wide-field astronomical surveys and terrestrial laboratories have jointly created a phase transition in the ecosystem of dark matter models and probes. Going forward, any robust understanding of dark matter requires astronomical observations, which still provide the only empirical evidence for dark matter to date. We have a unique opportunity right now to create a dark matter experiment with Rubin Observatory Legacy Survey of Space and Time (LSST). This experiment will be a coordinated effort to perform dark matter research, and provide a large collaborative team of scientists with the necessary organizational and funding supports. This approach leverages existing investments in Rubin. Studies of dark matter with Rubin LSST will also guide the design of, and confirm the results from, other dark matter experiments. Supporting a collaborative team to carry out a dark matter experiment with Rubin LSST is the key to achieving the dark matter science goals that have already been identified as high priority by the high-energy physics and astronomy communities