100 research outputs found
Star formation, quenching and chemical enrichment in local galaxies from integral field spectroscopy
Within the currently well-established ΛCDM cosmological framework we still lack a satisfactory un- derstanding of the processes that trigger, regulate and eventually quench star formation on galactic scales. Gas flows (including inflows from the cosmic web and supernovae-driven outflows) are con- sidered to act as self-regulatory mechanisms, generating the scaling relations between stellar mass, star formation rate and metallicity observed in the local Universe by large spectroscopic surveys. These surveys, however, have so far been limited by the availability of only one spectrum per galaxy. The aim of this dissertation is to expand the study of star formation and chemical abundances to resolved scales within galaxies by using integral field spectroscopy (IFS) data, mostly from the ongoing SDSS- IV MaNGA survey.
In the first part of this thesis I demonstrate the ubiquitous presence of extended low ionisation emission-line regions (LIERs) in both late- and early-type galaxies. By studying the Hα equivalent width and diagnostic line ratios radial profiles, together with tracers of the underlying stellar popula- tion, I show that LIERs are not due to a central point source but to hot evolved (post-asymptotic giant branch) stars. In light of this, I suggest a new classification scheme for galaxies based on their line emission. By analysing the colours, star formation rates, morphologies, gas and stellar kinematics and environmental properties of galaxies with substantial LIER emission, I identify two distinct popula- tions. Galaxies where the central regions are LIER-like, but show star formation at larger radii are late types in which star formation is slowly quenched inside-out. This transformation is associated with massive bulges. Galaxies dominated by LIER emission at all radii, on the other hand, are red-sequence galaxies harbouring a residual cold gas component, acquired mostly via external accretion. Quiescent galaxies devoid of line emission reside in denser environments, which suggests environmental effects as a likely cause for the existence of line-less galaxies on the red sequence.
In the second part of this dissertation I focus on the study of resolved chemical abundances by characterising the gas phase oxygen and nitrogen abundance gradients in a large sample of star forming galaxies. I analyse the deviations from an exponential profile at small and large radii and the dependence of the gradients on stellar mass. These findings are interpreted in the context of the inside-out paradigm of disc growth. I then demonstrate the necessity of gas flows, which are responsible for the observed flattening of the metallicity and N/O ratio gradients at large radii. Finally, I present a case study based on one nearby galaxy (NGC 628), in which I combine IFS and cold gas data to derive a spatially resolved metal budget and estimate the mass of metals lost by the galaxy throughout its life- time. By using simple physically-motivated models of chemical evolution I infer the average outflow loading factor to be of order unity.STF
Investigating the Drivers of Electron Temperature Variations in H ii Regions with Keck-KCWI and VLT-MUSE
H ii region electron temperatures are a critical ingredient in metallicity determinations, and recent observations have revealed systematic variations in the temperatures measured using different ions. We present electron temperatures (T e ) measured using the optical auroral lines ([N ii]λ5756, [O ii]λ λ7320, 7330, [S ii]λ λ4069, 4076, [O iii]λ4363, and [S iii]λ6312) for a sample of H ii regions in seven nearby galaxies. We use observations from the Physics at High Angular resolution in Nearby Galaxies survey (PHANGS) obtained with integral field spectrographs on Keck (Keck Cosmic Web Imager) and the Very Large Telescope (Multi-Unit Spectroscopic Explorer). We compare the different T e measurements with H ii region and ISM environmental properties such as electron density, ionization parameter, molecular gas velocity dispersion, and stellar association/cluster mass and age obtained from PHANGS. We find that the temperatures from [O ii] and [S ii] are likely overestimated due to the presence of electron density inhomogeneities in H ii regions. We measure high [O iii] temperatures in a subset of regions with high molecular gas velocity dispersion and low ionization parameter, which may be explained by the presence of low-velocity shocks. In agreement with previous studies, the T e–T e between [N ii] and [S iii] temperatures have the lowest observed scatter and follow predictions from photoionization modeling, which suggests that these tracers reflect H ii region temperatures across the various ionization zones better than [O ii], [S ii], and [O iii]
A Two-Component Probability Distribution Function Describes the mid-IR Emission from the Disks of Star-Forming Galaxies
High-resolution JWST-MIRI images of nearby spiral galaxies reveal emission
with complex substructures that trace dust heated both by massive young stars
and the diffuse interstellar radiation field. We present high angular (0."85)
and physical resolution (20-80 pc) measurements of the probability distribution
function (PDF) of mid-infrared (mid-IR) emission (7.7-21 m) from 19 nearby
star-forming galaxies from the PHANGS-JWST Cycle-1 Treasury. The PDFs of mid-IR
emission from the disks of all 19 galaxies consistently show two distinct
components: an approximately log-normal distribution at lower intensities and a
high-intensity power-law component. These two components only emerge once
individual star-forming regions are resolved. Comparing with locations of HII
regions identified from VLT/MUSE H-mapping, we infer that the power-law
component arises from star-forming regions and thus primarily traces dust
heated by young stars. In the continuum-dominated 21 m band, the power-law
is more prominent and contains roughly half of the total flux. At 7.7-11.3
m, the power-law is suppressed by the destruction of small grains
(including PAHs) close to HII regions while the log-normal component tracing
the dust column in diffuse regions appears more prominent. The width and shape
of the log-normal diffuse emission PDFs in galactic disks remain consistent
across our sample, implying a log-normal gas column density
(H)cm shaped by supersonic turbulence with typical
(isothermal) turbulent Mach numbers . Finally, we describe how the
PDFs of galactic disks are assembled from dusty HII regions and diffuse gas,
and discuss how the measured PDF parameters correlate with global properties
such as star-formation rate and gas surface density.Comment: 30 pages without appendix, 17 figures, (with appendix images of full
sample: 56 pages, 39 figures), accepted in A
The ALMOND Survey: Molecular cloud properties and gas density tracers across 25 nearby spiral galaxies with ALMA
We use new HCN(1-0) data from the ALMOND (ACA Large-sample Mapping Of Nearby
galaxies in Dense gas) survey to trace the kpc-scale molecular gas density
structure and CO(2-1) data from PHANGS-ALMA to trace the bulk molecular gas
across 25 nearby, star-forming galaxies. At 2.1 kpc scale, we measure the
density-sensitive HCN/CO line ratio and the SFR/HCN ratio to trace the star
formation efficiency in the denser molecular medium. At 150 pc scale, we
measure structural and dynamical properties of the molecular gas via CO(2-1)
line emission, which is linked to the lower resolution data using an
intensity-weighted averaging method. We find positive correlations (negative)
of HCN/CO (SFR/HCN) with the surface density, the velocity dispersion and the
internal turbulent pressure of the molecular gas. These observed correlations
agree with expected trends from turbulent models of star formation, which
consider a single free-fall time gravitational collapse. Our results show that
the kpc-scale HCN/CO line ratio is a powerful tool to trace the 150 pc scale
average density distribution of the molecular clouds. Lastly, we find
systematic variations of the SFR/HCN ratio with cloud-scale molecular gas
properties, which are incompatible with a universal star formation efficiency.
Overall, these findings show that mean molecular gas density, molecular cloud
properties and star formation are closely linked in a coherent way, and
observations of density-sensitive molecular gas tracers are a useful tool to
analyse these variations, linking molecular gas physics to stellar output
across galaxy discs.Comment: 48 pages, 40 figure
GPER mediates the angiocrine actions induced by IGF1 through the HIF-1α/VEGF pathway in the breast tumor microenvironment
The G protein estrogen receptor GPER/GPR30 mediates estrogen action in breast cancer cells as well as in breast cancer-associated fibroblasts (CAFs), which are key components of microenvironment driving tumor progression. GPER is a transcriptional target of hypoxia inducible factor 1 alpha (HIF-1α) and activates VEGF expression and angiogenesis in hypoxic breast tumor microenvironment. Furthermore, IGF1/IGF1R signaling, which has angiogenic effects, has been shown to activate GPER in breast cancer cells. We analyzed gene expression data from published studies representing almost 5000 breast cancer patients to investigate whether GPER and IGF1 signaling establish an angiocrine gene signature in breast cancer patients. Next, we used GPER-positive but estrogen receptor (ER)-negative primary CAF cells derived from patient breast tumours and SKBR3 breast cancer cells to investigate the role of GPER in the regulation of VEGF expression and angiogenesis triggered by IGF1. We performed gene expression and promoter studies, western blotting and immunofluorescence analysis, gene silencing strategies and endothelial tube formation assays to evaluate the involvement of the HIF-1α/GPER/VEGF signaling in the biological responses to IGF1. We first determined that GPER is co-expressed with IGF1R and with the vessel marker CD34 in human breast tumors (n = 4972). Next, we determined that IGF1/IGF1R signaling engages the ERK1/2 and AKT transduction pathways to induce the expression of HIF-1α and its targets GPER and VEGF. We found that a functional cooperation between HIF-1α and GPER is essential for the transcriptional activation of VEGF induced by IGF1. Finally, using conditioned medium from CAFs and SKBR3 cells stimulated with IGF1, we established that HIF-1α and GPER are both required for VEGF-induced human vascular endothelial cell tube formation. These findings shed new light on the essential role played by GPER in IGF1/IGF1R signaling that induces breast tumor angiogenesis. Targeting the multifaceted interactions between cancer cells and tumor microenvironment involving both GPCRs and growth factor receptors has potential in future combination anticancer therapies
Star Formation Laws and Efficiencies across 80 Nearby Galaxies
We measure empirical relationships between the local star formation rate
(SFR) and properties of the star-forming molecular gas on 1.5 kpc scales across
80 nearby galaxies. These relationships, commonly referred to as "star
formation laws," aim at predicting the local SFR surface density from various
combinations of molecular gas surface density, galactic orbital time, molecular
cloud free-fall time, and the interstellar medium dynamical equilibrium
pressure. Leveraging a multiwavelength database built for the PHANGS survey, we
measure these quantities consistently across all galaxies and quantify
systematic uncertainties stemming from choices of SFR calibrations and the
CO-to-H conversion factors. The star formation laws we examine show 0.3-0.4
dex of intrinsic scatter, among which the molecular Kennicutt-Schmidt relation
shows a 10% larger scatter than the other three. The slope of this
relation ranges , implying that the molecular gas
depletion time remains roughly constant across the environments probed in our
sample. The other relations have shallower slopes (),
suggesting that the star formation efficiency (SFE) per orbital time, the SFE
per free-fall time, and the pressure-to-SFR surface density ratio (i.e., the
feedback yield) may vary systematically with local molecular gas and SFR
surface densities. Last but not least, the shapes of the star formation laws
depend sensitively on methodological choices. Different choices of SFR
calibrations can introduce systematic uncertainties of at least 10-15% in the
star formation law slopes and 0.15-0.25 dex in their normalization, while the
CO-to-H conversion factors can additionally produce uncertainties of 20-25%
for the slope and 0.10-0.20 dex for the normalization.Comment: 10 pages main text + 2 appendices. ApJL in press. Data products
available at
https://www.canfar.net/storage/list/phangs/RELEASES/Sun_etal_2023 . Slides
summarizing key results can be found at
https://www.dropbox.com/s/5gsegexeo9n0t05/Sun_et_PHANGS_2023.pptx?dl=
Detecting Radio AGN Signatures in Red Geysers
A new class of quiescent galaxies harboring possible AGN-driven winds has been discovered using spatially resolved optical spectroscopy from the ongoing SDSS-IV MaNGA survey. These galaxies, termed "red geysers", constitute 5−10% of the local quiescent population and are characterized by narrow bisymmetric patterns in ionized gas emission features. Cheung et al. argued that these galaxies host large-scale AGN-driven winds that may play a role in suppressing star formation at late times. In this work, we test the hypothesis that AGN activity is ultimately responsible for the red geyser phenomenon. We compare the nuclear radio activity of the red geysers to a matched control sample with similar stellar mass, redshift, rest frame NUV−r color, axis ratio and presence of ionized gas. We have used the 1.4 GHz radio continuum data from VLA FIRST survey to stack the radio flux from the red geyser and control samples. In addition to a 3 times higher FIRST detection rate, we find that red geysers have a 5σ higher level of average radio flux than control galaxies. After restricting to rest-frame NUV−r color > 5 and checking mid-IR WISE photometry, we rule out star formation contamination and conclude that red geysers are associated with more active AGN. Red geysers and a possibly-related class with disturbed Hα emission account for 40\% of all radio-detected red galaxies with log (M⋆/M⊙)<11. Our results support a picture in which episodic AGN activity drives large-scale-relatively weak ionized winds that may provide a feedback mechanism for many early-type galaxies
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
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