| 1. |
- Dahlen, Tomas, et al.
(författare)
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Evolution of the luminosity function, star formation rate, morphology, and size of star-forming galaxies selected at rest-frame 1500 and 2800 angstrom
- 2007
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 654:1, s. 172-185
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Tidskriftsartikel (refereegranskat)abstract
- Using the multiwavelength photometric and spectroscopic data covering the Chandra Deep Field South obtained within the Great Observatories Origins Deep Survey, we investigate the rest-frame UV properties of galaxies to z similar to 2.2, including the evolution of the luminosity function, the luminosity density, star formation rate (SFR), and galaxy morphology. We find a significant brightening (similar to 1 mag) in the rest-frame 2800 angstrom characteristic magnitude (M*) over the redshift range 0.3 less than or similar to z less than or similar to 1.7 and no evolution at higher redshifts. The rest-frame 2800 angstrom luminosity density shows an increase by a factor of similar to 4 over the redshift range investigated. We estimate the SFR density to z similar to 2.2 from the 1500 and 2800 angstrom luminosities. When no correction for extinction is made, we find that the SFR derived from the 2800 angstrom luminosity density is almost a factor of 2 higher than that derived from the 1500 8 luminosities. Attributing this difference to differential dust extinction, we find that E(B - V) = 0.20 results in the same extinction-corrected SFR from both 1500 and 2800 angstrom luminosities. The extinction-corrected SFR is a factor of similar to 6.5 (similar to 3.7) higher than the uncorrected SFR derived from 1500 8 ( 2800 8) luminosity. We investigate the morphological composition of our sample by fitting Sersic profiles to the HST ACS galaxy images at a fixed rest-frame wavelength of 2800 angstrom at 0.5 less than or similar to z less than or similar to 2.2. We find that the fraction of apparently bulge-dominated galaxies (Sersic index n > 2.5) increases from similar to 10% at z similar to 0.5 to similar to 30% at z similar to 2.2. At the same time, we note that galaxies get bluer at increasing redshift. This suggests a scenario where an increased fraction of the star formation takes place in bulge-dominated systems at high redshift. This could be evidence that the present-day elliptical galaxies are a result of assembly (i.e., mergers) of galaxies at z greater than or similar to 1. Finally, we find that galaxy size for a luminosity-selected sample evolves as r(h) proportional to (1+z)(-1.1) between redshifts z = 2.2 and 1.1. This is consistent with previous measurements and suggests a similar evolution over the redshift range 0 less than or similar to z less than or similar to 6.
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| 2. |
- Hannon, Stephen, et al.
(författare)
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Star cluster classification using deep transfer learning with PHANGS-HST
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 526:2, s. 2991-3006
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Tidskriftsartikel (refereegranskat)abstract
- Currently available star cluster catalogues from the Hubble Space Telescope (HST) imaging of nearby galaxies heavily rely on visual inspection and classification of candidate clusters. The time-consuming nature of this process has limited the production of reliable catalogues and thus also post-observation analysis. To address this problem, deep transfer learning has recently been used to create neural network models that accurately classify star cluster morphologies at production scale for nearby spiral galaxies (D ≲ 20 Mpc). Here, we use HST ultraviolet (UV)–optical imaging of over 20 000 sources in 23 galaxies from the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) survey to train and evaluate two new sets of models: (i) distance-dependent models, based on cluster candidates binned by galaxy distance (9–12, 14–18, and 18–24 Mpc), and (ii) distance-independent models, based on the combined sample of candidates from all galaxies. We find that the overall accuracy of both sets of models is comparable to previous automated star cluster classification studies (∼60–80 per cent) and shows improvement by a factor of 2 in classifying asymmetric and multipeaked clusters from PHANGS-HST. Somewhat surprisingly, while we observe a weak negative correlation between model accuracy and galactic distance, we find that training separate models for the three distance bins does not significantly improve classification accuracy. We also evaluate model accuracy as a function of cluster properties such as brightness, colour, and spectral energy distribution (SED)-fit age. Based on the success of these experiments, our models will provide classifications for the full set of PHANGS-HST candidate clusters (N ∼ 200 000) for public release.
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| 3. |
- Kuschel, Maxwell, et al.
(författare)
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Investigating the Dominant Environmental Quenching Process in UVCANDELS/COSMOS Groups
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 947:1
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Tidskriftsartikel (refereegranskat)abstract
- We explore how the fraction of quenched galaxies changes in groups of galaxies with respect to the distance to the center of the group, redshift, and stellar mass to determine the dominant process of environmental quenching in 0.2 < z < 0.8 groups. We use new UV data from the UVCANDELS project in addition to existing multiband photometry to derive new galaxy physical properties of the group galaxies from the zCOSMOS 20 k group catalog. Limiting our analysis to a complete sample of log (M*/M⊙) > 10.56 group galaxies, we find that the probability of being quenched increases slowly with decreasing redshift, diverging from the stagnant field galaxy population. A corresponding analysis on how the probability of being quenched increases with time within groups suggests that the dominant environmental quenching process is characterized by slow (∼Gyr) timescales. We find a quenching time of approximately Gyr, consistent with the slow processes of strangulation and delayed-then-rapid quenching although more data are needed to confirm this result.
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| 4. |
- Martin, Alec, et al.
(författare)
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UV-bright Star-forming Clumps and Their Host Galaxies in UVCANDELS at 0.5 ≤ z ≤ 1
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 955:2
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Tidskriftsartikel (refereegranskat)abstract
- Giant star-forming clumps are a prominent feature of star-forming galaxies (SFGs) and contain important clues on galaxy formation and evolution. However, the basic demographics of clumps and their host galaxies remain uncertain. Using the Hubble Space Telescope/Wide Field Camera 3 F275W images from the Ultraviolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we detect and analyze giant star-forming clumps in galaxies at 0.5 ≤ z ≤ 1, connecting two epochs when clumps are common (at cosmic high noon, z ∼ 2) and rare (in the local Universe). We construct a clump sample whose rest-frame 1600 Å luminosity is 3 times higher than the most luminous local H ii regions (MUV ≤ −16 AB). In our sample, 35% ± 3% of low-mass galaxies (log[M∗/M⊙] < 10) are clumpy (i.e., containing at least one off-center clump). This fraction changes to 22% ± 3% and 22% ± 4% for intermediate (10 ≤ log[M∗/M⊙] ≤ 10.5) and high-mass (log[M∗/M⊙] > 10.5) galaxies, in agreement with previous studies. When compared to similar-mass nonclumpy SFGs, low- and intermediate-mass clumpy SFGs tend to have higher star formation rates (SFRs) and bluer rest-frame U − V colors, while high-mass clumpy SFGs tend to be larger than nonclumpy SFGs. However, clumpy and nonclumpy SFGs have similar Sérsic index, indicating a similar underlying density profile. Furthermore, we investigate how the UV luminosity of star-forming regions correlates with the physical properties of host galaxies. On average, more luminous star-forming regions reside in more luminous, smaller, and/or higher specific SFR galaxies and are found closer to their hosts' galactic centers.
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| 5. |
- Sattari, Zahra, et al.
(författare)
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Fraction of Clumpy Star-forming Galaxies at 0.5 ≤ z ≤ 3 in UVCANDELS : Dependence on Stellar Mass and Environment
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 951:2
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution imaging of galaxies in rest-frame UV has revealed the existence of giant star-forming clumps prevalent in high-redshift galaxies. Studying these substructures provides important information about their formation and evolution and informs theoretical galaxy evolution models. We present a new method to identify clumps in galaxies' high-resolution rest-frame UV images. Using imaging data from CANDELS and UVCANDELS, we identify star-forming clumps in an HST/F160W ≤ 25 AB mag sample of 6767 galaxies at 0.5 ≤ z ≤ 3 in four fields, GOODS-N, GOODS-S, EGS, and COSMOS. We use a low-passband filter in Fourier space to reconstruct the background image of a galaxy and detect small-scale features (clumps) on the background-subtracted image. Clumpy galaxies are defined as those having at least one off-center clump that contributes a minimum of 10% of the galaxy's total rest-frame UV flux. We measure the fraction of clumpy galaxies (fclumpy) as a function of stellar mass, redshift, and galaxy environment. Our results indicate that fclumpy increases with redshift, reaching ∼65% at z ∼ 1.5. We also find that fclumpy in low-mass galaxies () is 10% higher compared to that of their high-mass counterparts (). Moreover, we find no evidence of significant environmental dependence of fclumpy for galaxies at the redshift range of this study. Our results suggest that the fragmentation of gas clouds under violent disk instability remains the primary driving mechanism for clump formation, and incidents common in dense environments, such as mergers, are not the dominant processes.
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