- ID:
- ivo://CDS.VizieR/J/ApJ/846/145
- Title:
- PHAT. XIX. Formation history of M31 disk
- Short Name:
- J/ApJ/846/145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We map the star formation history across M31 by fitting stellar evolution models to color-magnitude diagrams of each 83"x83" (0.3x1.4kpc, deprojected) region of the Panchromatic Hubble Andromeda Treasury (PHAT) survey outside of the innermost 6'x12' portion. We find that most of the star formation occurred prior to ~8Gyr ago, followed by a relatively quiescent period until ~4Gyr ago, a subsequent star formation episode about 2Gyr ago, and a return to relative quiescence. There appears to be little, if any, structure visible for populations with ages older than 2Gyr, suggesting significant mixing since that epoch. Finally, assuming a Kroupa initial mass function from 0.1 to 100M_{sun}_, we find that the total amount of star formation over the past 14Gyr in the area over which we have fit models is 5x10^10^M_{sun}_. Fitting the radial distribution of this star formation and assuming azimuthal symmetry, (1.5+/-0.2)x10^11^M_{sun}_ of stars has formed in the M31 disk as a whole, (9+/-2)x10^10^M_{sun}_ of which has likely survived to the present after accounting for evolutionary effects. This mass is about one-fifth of the total dynamical mass of M31.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/215/9
- Title:
- PHAT X. UV-IR photometry of M31 stars
- Short Name:
- J/ApJS/215/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have measured stellar photometry with the Hubble Space Telescope Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys in near ultraviolet (F275W, F336W), optical (F475W, F814W), and near infrared (F110W, F160W) bands for 117 million resolved stars in M31. As part of the Panchromatic Hubble Andromeda Treasury survey, we measured photometry with simultaneous point-spread function (PSF) fitting across all bands and at all source positions after precise astrometric image alignment (<5-10mas accuracy). In the outer disk, the photometry reaches a completeness-limited depth of F475W~28, while in the crowded, high surface brightness bulge, the photometry reaches F475W~25. We find that simultaneous photometry and optimized measurement parameters significantly increase the detection limit of the lowest-resolution filters (WFC3/IR) providing color-magnitude diagrams (CMDs) that are up to 2.5mag deeper when compared with CMDs from WFC3/IR photometry alone. We present extensive analysis of the data quality including comparisons of luminosity functions and repeat measurements, and we use artificial star tests to quantify photometric completeness, uncertainties and biases. We find that the largest sources of systematic error in the photometry are due to spatial variations in the PSF models and charge transfer efficiency corrections.
- ID:
- ivo://CDS.VizieR/J/ApJ/827/33
- Title:
- PHAT. XVI. Star cluster masses and ages
- Short Name:
- J/ApJ/827/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Panchromatic Hubble Andromeda Treasury survey data set to perform spatially resolved measurements of star cluster formation efficiency ({Gamma}), the fraction of stellar mass formed in long-lived star clusters. We use robust star formation history and cluster parameter constraints, obtained through color-magnitude diagram analysis of resolved stellar populations, to study Andromeda's cluster and field populations over the last ~300Myr. We measure {Gamma} of 4%-8% for young, 10-100Myr-old populations in M31. We find that cluster formation efficiency varies systematically across the M31 disk, consistent with variations in mid-plane pressure. These {Gamma} measurements expand the range of well-studied galactic environments, providing precise constraints in an HI-dominated, low-intensity star formation environment. Spatially resolved results from M31 are broadly consistent with previous trends observed on galaxy-integrated scales, where {Gamma} increases with increasing star formation rate surface density ({Sigma}_SFR_). However, we can explain observed scatter in the relation and attain better agreement between observations and theoretical models if we account for environmental variations in gas depletion time ({tau}_dep_) when modeling {Gamma}, accounting for the qualitative shift in star formation behavior when transitioning from a H_2_-dominated to a HI-dominated interstellar medium. We also demonstrate that {Gamma} measurements in high {Sigma}_SFR_ starburst systems are well-explained by {tau}_dep_-dependent fiducial {Gamma} models.
- ID:
- ivo://CDS.VizieR/J/ApJ/768/74
- Title:
- PHIBSS: CO observations of star-forming galaxies
- Short Name:
- J/ApJ/768/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO(3-2) survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z~1.2 and 2.2, with log(M_*_(M_{sun}_))>=10.4 and log(SFR(M_{sun}_/yr))>=1.5. Including a correction for the incomplete coverage of the M_*_-SFR plane, and adopting a "Galactic" value for the CO-H_2_ conversion factor, we infer average gas fractions of ~0.33 at z~1.2 and ~0.47 at z~2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z~1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z=1-3 SFGs is near-linear, with a ~0.7Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z~0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M_*_, gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z~0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.
- ID:
- ivo://CDS.VizieR/J/AJ/125/465
- Title:
- Phoenix Deep Survey 1.4-GHz microJy Catalog
- Short Name:
- J/AJ/125/465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The initial Phoenix Deep Survey (PDS) observations with the Australia Telescope Compact Array have been supplemented by additional 1.4 GHz observations over the past few years. Here we present details of the construction of a new mosaic image covering an area of 4.56 deg2, an investigation of the reliability of the source measurements, and the 1.4 GHz source counts for the compiled radio catalog. The mosaic achieves a 1-sigma rms noise of 12 microJy at its most sensitive, and a homogeneous radio-selected catalog of over 2000 sources reaching flux densities as faint as 60 microJy has been compiled. The source parameter measurements are found to be consistent with the expected uncertainties from the image noise levels and the Gaussian source fitting procedure. A radio-selected sample avoids the complications of obscuration associated with optically selected samples, and by utilizing complementary PDS observations, including multicolor optical, near-infrared, and spectroscopic data, this radio catalog will be used in a detailed investigation of the evolution in star formation spanning the redshift range 0 < z < 1. The homogeneity of the catalog ensures a consistent picture of galaxy evolution can be developed over the full cosmologically significant redshift range of interest.
- ID:
- ivo://CDS.VizieR/J/ApJS/155/1
- Title:
- Phoenix Deep Survey: optical and NIR catalogs
- Short Name:
- J/ApJS/155/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Phoenix Deep Survey is a multiwavelength galaxy survey based on deep 1.4GHz radio imaging. The primary goal of this survey is to investigate the properties of star formation in galaxies and to trace the evolution in those properties to a redshift z=1, covering a significant fraction of the age of the universe. By compiling a sample of star-forming galaxies based on selection at radio wavelengths we eliminate possible biases due to dust obscuration, a significant issue when selecting objects at optical and ultraviolet wavelengths. In this paper, we present the catalogs and results of deep optical (UBVRI) and near-infrared (Ks) imaging of the deepest region of the existing decimetric radio imaging. The observations and data processing are summarized and the construction of the optical source catalogs described, together with the details of the identification of candidate optical counterparts to the radio catalogs. Based on our UBVRIKs imaging, photometric redshift estimates for the optical counterparts to the radio detections are explored.
- ID:
- ivo://CDS.VizieR/J/ApJ/624/135
- Title:
- Phoenix Deep Survey spectroscopic catalog
- Short Name:
- J/ApJ/624/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Phoenix Deep Survey is a multiwavelength survey based on deep 1.4GHz radio imaging, reaching well into the sub-100uJy level. One of the aims of this survey is to characterize the submillijansky radio population, exploring its nature and evolution. In this paper we present the catalog and results of the spectroscopic observations aimed at characterizing the optically "bright" (R<~21.5mag) counterparts of faint radio sources. Of 371 sources with redshift determination, 21% have absorption lines only, 11% show active galactic nucleus signatures, 32% are star-forming galaxies, 34% show narrow emission lines that do not allow detailed spectral classification (owing to poor signal-to-noise ratio and/or lack of diagnostic emission lines), and the remaining 2% are identified with stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/466/2006
- Title:
- Phoenix dwarf galaxy RV and [Fe/H] catalog
- Short Name:
- J/MNRAS/466/2006
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Transition type dwarf galaxies are thought to be systems undergoing the process of transformation from a star-forming into a passively evolving dwarf, which makes them particularly suitable to study evolutionary processes driving the existence of different dwarf morphological types. Here we present results from a spectroscopic survey of ~200 individual red giant branch stars in the Phoenix dwarf, the closest transition type with a comparable luminosity to 'classical' dwarf galaxies. We measure a systemic heliocentric velocity Vhelio=-21.2+/-1.0km/s. Our survey reveals the clear presence of prolate rotation that is aligned with the peculiar spatial distribution of the youngest stars in Phoenix. We speculate that both features might have arisen from the same event, possibly an accretion of a smaller system. The evolved stellar population of Phoenix is relatively metal-poor (<[Fe/H]>=-1.49+/-0.04dex) and shows a large metallicity spread (sigma_[Fe/H]_=0.51+/-0.04dex), with a pronounced metallicity gradient of -0.13+/-0.01dex/arcmin similar to luminous, passive dwarf galaxies. We also report a discovery of an extremely metal-poor star candidate in Phoenix and discuss the importance of correcting for spatial sampling when interpreting the chemical properties of galaxies with metallicity gradients. This study presents a major leap forward in our knowledge of the internal kinematics of the Phoenix transition type dwarf galaxy and the first wide area spectroscopic survey of its metallicity properties.
- ID:
- ivo://CDS.VizieR/J/MNRAS/416/2
- Title:
- Photodissociation regions in M33
- Short Name:
- J/MNRAS/416/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive total (atomic + molecular) hydrogen densities in giant molecular clouds (GMCs) in the nearby spiral galaxy M33 using a method that views the atomic hydrogen near regions of recent star formation as the product of photodissociation. Far-ultraviolet (FUV) photons emanating from a nearby OB association produce a layer of atomic hydrogen on the surfaces of nearby GMCs. Our approach provides an estimate of the total hydrogen density in these GMCs from observations of the excess FUV emission that reaches the GMC from the OB association and of the excess 21-cm radio HI emission produced after these FUV photons convert H2 into HI on the GMC surface. The method provides an alternative approach to the use of CO emission as a tracer of H2 in GMCs and is especially sensitive to a range of densities well below the critical density for CO(1-0) emission.
- ID:
- ivo://CDS.VizieR/J/A+A/574/A127
- Title:
- Photodissociation with mechanical heating
- Short Name:
- J/A+A/574/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CO observations in active galactic nuclei and starbursts reveal high kinetic temperatures. Those environments are thought to be very turbulent due to dynamic phenomena, such as outflows and high supernova rates. We investigate the effect of mechanical heating on atomic fine-structure and molecular lines and on their ratios. We try to use those ratios as a diagnostic to constrain the amount of mechanical heating in an object and also study its significance on estimating the H_2_ mass. Equilibrium photodissociation models (PDRs hereafter) were used to compute the thermal and chemical balance for the clouds. The equilibria were solved for numerically using the optimized version of the Leiden PDR-XDR code. Large velocity-gradient calculations were done as post-processing on the output of the PDR models using RADEX. High-J CO line ratios are very sensitive to mechanical heating ({GAMMA}mech hereafter). Emission becomes at least one order of magnitude brighter in clouds with n~10^5^cm^-3^ and a star formation rate of 1M_{sun}/yr (corresponding to {GAMMA}mech=2x10^-19^erg/cm^3^/s). The Emission of low-J CO lines is not as sensitive to {GAMMA}mech, but they do become brighter in response to {GAMMA}mech. Generally, for all of the lines we considered, {GAMMA}mech increases excitation temperatures and decreases the optical depth at the line centre. Hence line ratios are also effected, strongly in some cases. Ratios involving HCN are a good diagnostic for {GAMMA}mech , where the HCN(1-0)/CO(1-0) increases from 0.06 to 0.25, and the HCN(1-0)/HCO^+^ (1-0) increase from 0.15 to 0.5 for amounts of {GAMMA}mech that are equivalent to 5% of the surface heating rate. Both ratios increase to more than 1 for higher {GAMMA}mech , as opposed to being much less than unity in pure PDRs. The first major conclusion is that low-J to high-J intensity ratios will yield a good estimate of the mechanical heating rate (as opposed to only low-J ratios). The second one is that the mechanical heating rate should be taken into account when determining AV or, equivalently, NH, and consequently the cloud mass. Ignoring {GAMMA}mech will also lead to large errors in density and radiation field estimates.
