We present and describe the astro-photometric catalog of more than 800,000 sources found in the Hubble Tarantula Treasury Project (HTTP). HTTP is a Hubble Space Telescope Treasury program designed to ...image the entire 30 Doradus region down to the sub-solar (~0.5 M sub(middot in circle)) mass regime using the Wide Field Camera 3 and the Advanced Camera for Surveys. We observed 30 Doradus in the near-ultraviolet (F275W, F336W), optical (F555W, F658N, F775W), and near-infrared (F110W, F160W) wavelengths. The stellar photometry was measured using point-spread function fitting across all bands simultaneously. The relative astrometric accuracy of the catalog is 0.4 mas. The astro-photometric catalog, results from artificial star experiments, and the mosaics for all the filters are available for download. Color-magnitude diagrams are presented showing the spatial distributions and ages of stars within 30 Dor as well as in the surrounding fields. HTTP provides the first rich and statistically significant sample of intermediate- and low-mass pre-main sequence candidates and allows us to trace how star formation has been developing through the region. The depth and high spatial resolution of our analysis highlight the dual role of stellar feedback in quenching and triggering star formation on the giant H II region scale. Our results are consistent with stellar sub-clustering in a partially filled gaseous nebula that is offset toward our side of the Large Magellanic Cloud.
A previous spectroscopic study identified the very massive O2 III star VFTS 16 in the Tarantula Nebula as a runaway star based on its peculiar line-of-sight velocity. We use the Gaia DR2 catalog to ...measure the relative proper motion of VFTS 16 and nearby bright stars to test if this star might have been ejected from the central cluster, R136, via dynamical ejection. We find that the position angle and magnitude of the relative proper motion (0.338±0.046 mas yr−1, or approximately 80±11 km s−1) of VFTS 16 are consistent with ejection from R136 approximately 1.5±0.2 Myr ago, very soon after the cluster was formed. There is some tension with the presumed age of VFTS 16 that, from published stellar parameters, cannot be greater than 0.9+0.3−0.2 0.9 − 0.2 + 0.3 $ 0.9^{+0.3}_{-0.2} $ Myr. Older ages for this star would appear to be prohibited due to the absence of He I lines in its optical spectrum, since this sets a firm lower limit on its effective temperature. The dynamical constraints may imply an unusual evolutionary history for this object, perhaps indicating it is a merger product. Gaia DR2 also confirms that another very massive star in the Tarantula Nebula, VFTS 72 (alias BI 253; O2 III-V(n)((f*)), is also a runaway on the basis of its proper motion as measured by Gaia. While its tangential proper motion (0.392±0.062 mas yr−1 or 93±15 km s−1) would be consistent with dynamical ejection from R136 approximately 1 Myr ago, its position angle is discrepant with this direction at the 2σ level. From their Gaia DR2 proper motions we conclude that the two ∼100 M⊙ O2 stars, VFTS 16 and VFTS 72, are fast runaway stars, with space velocities of around 100 km s−1 relative to R136 and the local massive star population. The dynamics of VFTS 16 are consistent with it having been ejected from R136, and this star therefore sets a robust lower limit on the age of the central cluster of ∼1.3 Myr.
We present the results of a systematic search for galaxies in the redshift range z= 6–9, within the new, deep, near-infrared (Y, J, H) imaging of the Hubble Ultra Deep Field provided by the Wide ...Field Camera 3 (WFC3) on the Hubble Space Telescope. We have performed full spectral energy distribution fitting to the optical+infrared photometry of all high-redshift galaxy candidates detected at ≥5σ significance in at least one of the WFC3/IR broad-band filters. After careful rejection of contaminants, the result is a sample of 49 galaxies with primary photometric redshift solutions z > 5.9, within the 4.5 arcmin2 field covered by the new near-infrared imaging. Our sample, selected without recourse to specific colour cuts, reselects all but the faintest one of the 16 z850-drops selected by Oesch et al., recovers all five of the Y105-drops reported by Bouwens et al. and adds a further 29 equally plausible galaxy candidates, of which 12 lie beyond z≃ 6.3 and four lie beyond z≃ 7.0. However, we also present confidence intervals on our photometric redshift estimates, including alternative secondary redshift solutions. As a result of this analysis, we caution that acceptable low-redshift (z < 2) solutions exist for 28 out of the 37 galaxies at z > 6.3 and in particular for all eight of the galaxy candidates reported here at z > 7.5. Nevertheless, we note that the very highest redshift candidates appear to be strongly clustered in the field. Based on our photometric redshift analysis, we derive new estimates of the ultraviolet galaxy luminosity function at z≃ 7 and 8. Where our results are most robust, at a characteristic luminosity M1500≃−19.5 (AB), we find that the comoving number density of galaxies declines by a factor of ≃2.5 between z≃ 6 and 7 and by a further factor of ≃2 by z≃ 8. These results suggest that it is difficult for the observed population of high-redshift star-forming galaxies to achieve re-ionization by z≃ 6 without a significant contribution from galaxies well below the detection limits, plus alterations in the escape fraction of ionizing photons and/or continued vigorous star formation at z > 15.
ABSTRACT We present 12CO and 13CO molecular gas data observed by ALMA, massive early-stage young stellar objects (YSOs) identified by applying color-magnitude cuts to Spitzer and Herschel photometry, ...and low-mass late-stage YSOs identified via excess. Using dendrograms, we derive properties for the molecular cloud structures. This is the first time a dendrogram analysis has been applied to extragalactic clouds. The majority of clumps have a virial parameter equal to unity or less. The size-linewidth relations of 12CO and 13CO show the clumps in this study have a larger linewidth for a given size (by factors of 3.8 and 2.5, respectively) in comparison to several, but not all, previous studies. The larger linewidths in 30 Doradus compared to typical Milky Way quiescent clumps are probably due to the former's highly energetic environmental conditions. The slopes of the size-linewidth relations of 12CO, 0.65 0.04, and 13CO, 0.97 0.12, are on the higher end but consistent within 3 of those of previous studies. Massive star formation occurs in clumps with high masses (>1.83 × 102 M ), high linewidths (v > 1.18 km s−1), and high mass densities (>6.67 × 102 M pc−2). The majority of embedded, massive YSOs are associated with a clump; however, the majority of more evolved, low-mass YSOs are not.
ABSTRACT The Legacy ExtraGalactic UV Survey (LEGUS) is a Cycle 21 Treasury program on the Hubble Space Telescope aimed at the investigation of star formation and its relation with galactic ...environment in nearby galaxies, from the scales of individual stars to those of ∼kiloparsec-size clustered structures. Five-band imaging from the near-ultraviolet to the I band with the Wide-Field Camera 3 (WFC3), plus parallel optical imaging with the Advanced Camera for Surveys (ACS), is being collected for selected pointings of 50 galaxies within the local 12 Mpc. The filters used for the observations with the WFC3 are F275W(λ2704 ), F336W(λ3355 ), F438W(λ4325 ), F555W(λ5308 ), and F814W(λ8024 ); the parallel observations with the ACS use the filters F435W(λ4328 ), F606W(λ5921 ), and F814W(λ8057 ). The multiband images are yielding accurate recent ( 50 Myr) star formation histories from resolved massive stars and the extinction-corrected ages and masses of star clusters and associations. The extensive inventories of massive stars and clustered systems will be used to investigate the spatial and temporal evolution of star formation within galaxies. This will, in turn, inform theories of galaxy evolution and improve the understanding of the physical underpinning of the gas-star formation relation and the nature of star formation at high redshift. This paper describes the survey, its goals and observational strategy, and the initial scientific results. Because LEGUS will provide a reference survey and a foundation for future observations with the James Webb Space Telescope and with ALMA, a large number of data products are planned for delivery to the community.
Abstract
The Legacy ExtraGalactic UV Survey (LEGUS) is a multiwavelength Cycle 21 Treasury program on the
Hubble Space Telescope
. It studied 50 nearby star-forming galaxies in 5 bands from the ...near-UV to the I-band, combining new Wide Field Camera 3 observations with archival Advanced Camera for Surveys data. LEGUS was designed to investigate how star formation occurs and develops on both small and large scales, and how it relates to the galactic environments. In this paper we present the photometric catalogs for all the apparently single stars identified in the 50 LEGUS galaxies. Photometric catalogs and mosaicked images for all filters are available for download. We present optical and near-UV color–magnitude diagrams for all the galaxies. For each galaxy we derived the distance from the tip of the red giant branch. We then used the NUV color–magnitude diagrams to identify stars more massive than 14
M
⊙
, and compared their number with the number of massive stars expected from the
GALEX
FUV luminosity. Our analysis shows that the fraction of massive stars forming in star clusters and stellar associations is about constant with the star formation rate. This lack of a relation suggests that the timescale for evaporation of unbound structures is comparable or longer than 10 Myr. At low star formation rates this translates to an excess of mass in clustered environments as compared to model predictions of cluster evolution, suggesting that a significant fraction of stars form in unbound systems.
We present a study of the recent star formation (SF) of 30 Doradus in the Large Magellanic Cloud (LMC) using the panchromatic imaging survey Hubble Tarantula Treasury Project. In this paper we focus ...on the stars within 20 pc of the center of 30 Doradus, the starburst region NGC 2070. We recovered the SF history by comparing deep optical and near-infrared color–magnitude diagrams (CMDs) with state-of-the-art synthetic CMDs generated with the latest PAdova and TRieste Stellar Evolution Code (PARSEC) models, which include all stellar phases from pre-main-sequence to post-main-sequence. For the first time in this region we are able to measure the SF using intermediate- and low-mass stars simultaneously. Our results suggest that NGC 2070 experienced prolonged activity. In particular, we find that the SF in the region (1) exceeded the average LMC rate ≈ 20 Myr ago, (2) accelerated dramatically ≈ 7 Myr ago, and (3) reached a peak value 1–3 Myr ago. We did not find significant deviations from a Kroupa initial mass function down to 0.5 M{sub ⊙}. The average internal reddening E(B−V) is found to be between 0.3 and 0.4 mag.
Abstract
We derive the recent star formation histories (SFHs) of 23 active dwarf galaxies using
Hubble Space Telescope
observations from the Legacy Extragalactic UV Survey. We apply a color–magnitude ...diagram (CMD) fitting technique using two independent sets of stellar models, PARSEC-COLIBRI and MIST. Despite the nonnegligible recent activity, none of the 23 star-forming dwarfs show enhancements in the last 100 Myr larger than three times the 100 Myr average. The unweighted mean of the individual SFHs in the last 100 Myr is also consistent with a rather constant activity, irrespective of the atomic gas fraction. We confirm previous results that for dwarf galaxies, the CMD-based average star formation rates (SFRs) are generally higher than the FUV-based SFRs. For half of the sample, the 60 Myr average CMD-based SFR is more than two times the FUV SFR. In contrast, we find remarkable agreement between the 10 Myr average CMD-based SFR and the H
α
-based SFR. Finally, using core helium-burning stars of intermediate mass, we study the pattern of star formation spatial progression over the past 60 Myr and speculate on the possible triggers and connections of the star formation activity with the environment in which these galaxies live. Approximately half of our galaxies show spatial progression of star formation in the last 60 Myr and/or very recent diffuse and off-center activity compared to RGB stars.
We derive the star formation history (SFH) in four regions of the Small Magellanic Cloud (SMC) using the deepest VI color-magnitude diagrams (CMDs) ever obtained for this galaxy. The images were ...obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope (HST) and are located at projected distances of 0degrees.5-2degrees from the SMC center, probing the main body and the wing of the galaxy. We derived the SFHs of the four fields using two independent procedures to fit synthetic CMDs to the data. We compare the SFHs derived here with our earlier results for the SMC bar to create a deep pencil-beam survey of the global history of the central SMC. We find in all the six fields observed with HST a slow star formation (SF) pace from 13 to 5-7 Gyr ago, followed by a approx =2-3 times higher activity. This is remarkable because dynamical models do not predict a strong influence of either the Large Magellanic Cloud (LMC) or the Milky Way at that time. The level of the intermediate-age SF rate enhancement systematically increases toward the center, resulting in a gradient in the mean age of the population, with the bar fields being systematically younger than the outer ones. SF over the most recent 500 Myr is strongly concentrated in the bar, the only exception being the area of the SMC wing. The strong current activity of the latter is likely driven by interaction with the LMC. At a given age, there is no significant difference in metallicity between the inner and outer fields, implying that metals are well mixed throughout the SMC. The age-metallicity relations we infer from our best-fitting models are monotonically increasing with time, with no evidence of dips. This may argue against the major merger scenario proposed by Tsujimoto and Bekki in 2009, although a minor merger cannot be ruled out.