Beena Meena

The Galaxy UV Legacy Project (GULP) is a Cycle 28 Treasury program with the Hubble Space Telescope designed to characterize resolved massive stars, OB associations, and young star clusters in 26 nearby star-forming galaxies. Utilizing the Advanced Camera for Surveys/Solar Blind Channel F150LP and WFC3/UVIS F218W filters, combined with extensive archival observations, GULP provides an unprecedented panchromatic eight-band view from the far-UV to the I band. The target galaxies were carefully selected to span a broad range of metallicities, masses, morphological types, and star formation rates, thereby enabling detailed studies of star formation processes across different galactic environments. This paper introduces the GULP survey, detailing its observational strategy, data processing, and initial scientific results for the irregular barred starburst dwarf galaxy NGC 4449, used as a test case. We derived the physical parameters and ages for thousands of stars using the Binary Populations And Spectral Synthesis models, and found that the younger stars and clusters are predominantly concentrated along the galaxy’s central bar, and that over the past λ 2175 correlates with the intensity of the UV radiation. The “UV bump” is detected in many areas of the galaxy, but is absent in the regions of most intense and recent star formation. This strongly supports the scenario where UV radiation from young, massive stars effectively destroys the small dust grains responsible for the “UV bump.”

Compact galaxy groups are ideal laboratories for studying the effects of interactions between active galactic nuclei (AGN) and multiple nearby galaxies. Recent JWST observations of the nearby compact group Stephan’s Quintet highlight tidal flows between the interacting galaxies as well as outflows from the active galaxy NGC 7319. To study the kinematics on a large scale throughout the group, we obtained spatially resolved long-slit spectra of Stephan’s Quintet at multiple slit positions with Apache Point Observatory’s Kitt Peak Ohio State Multi-Object Spectrograph. We fit multiple Gaussians to the H α λ 6563 and [N II ] λλ 6548, 6583 emission lines to isolate the different kinematic components. We used the kinematics to develop the first biconical outflow model of the narrow-line region of NGC 7319. Using a combination of galactic rotation models, biconical outflow models, and kinematic maps of the ionized gas, we disentangled the outflows, rotation, and tidal flows in the group. We found outflow radial velocities up to 550 km s ⁻¹ peaking at 2.6 kpc from the central supermassive black hole, and a transition from AGN-powered outflows to gravitationally powered tidal flows at a projected distance between 2.4 and 6.3 kpc. We performed a line ratio analysis and determined the gas shows Seyfert-like ionization out to 6.3 kpc (projected), which supports our finding that gas outside this radius is predominantly powered by tidal flows. Our separation of kinematic components in Stephan’s Quintet will enable future studies of the physical conditions and dynamical forces in the ionized gas to better quantify the feeding and feedback processes of AGN in compact groups.

Context. There is considerable debate about the formation of massive stars, including whether a high-mass star must always form with a population of low-mass stars, or if it can also form in isolation. Massive stars found in the field are often considered to be runaways from star clusters or OB associations. However, there is evidence in the Milky Way and the Small Magellanic Cloud of high-mass stars that appear to be isolated in the field and they cannot be related to any known star cluster or OB association. Studies of more distant galaxies have been lacking so far. Aims. We identified massive star candidates that appear isolated in the field of the nearby spiral galaxy NGC 4242 (at a distance of 5.3 Mpc) to explore how many candidates for isolated star formation we find in a galaxy outside the Local Group. Methods. We identified 234 massive ( M _ini ≥ 15 M _⊙ ) and young (≤10 Myr) field stars in NGC 4242 using the Hubble Space Telescope Solar Blind Channel of the Advanced Camera for Surveys, the UVIS channel of the Wide Field Camera 3 from the Galaxy UV Legacy Project (GULP), and optical data from the Legacy ExtraGalactic UV Survey (LEGUS). We investigated the surroundings of our targets within the range of projected distances expected for runaway stars, 74 pc and 204 pc. Results. Within the threshold radii, 9.8% and 34.6% of our targets have no young star clusters, OB associations, or massive stars. This causes them to appear isolated. This fraction reduces to 3.2%−11.5% for the total number of massive stars expected from the observed UV star formation rate. Conclusions. Our results show that there is a small population of young and massive potentially isolated field stars in NGC 4242.

We present spatially resolved mass outflow rates of the ionized and molecular gas in the narrow-line region of the Seyfert 1 galaxy NGC 3227. Using long-slit spectroscopy and [O III ] imaging from from the Hubble Space Telescope’s Space Telescope Imaging Spectrograph and Apache Point Observatory’s Kitt Peak Ohio State Multi-Object Spectrograph, in conjunction with Cloudy photoionization models and emission-line diagnostics, we find a peak ionized mass outflow rate of M ̇ ion = 19.9 ± 9.2 M _⊙ yr ⁻¹ at a distance of 47 ± 6 pc from the supermassive black hole (SMBH). Using archival data from the Gemini-North Near-infrared Field Spectrograph measuring H ₂ 2.1218 μ m emission, we find a maximum peak warm molecular outflow rate of M ̇ H 2 ≤ 9 × 10 − 4 M _⊙ yr ⁻¹ at a distance of 36 ± 6 pc from the SMBH. Using archival data from the Atacama Large Millimeter/submillimeter Array measuring CO(2–1) emission, we find a maximum peak cold molecular gas mass outflow rate of M ̇ CO ≤ 23.1 M _⊙ yr ⁻¹ at a distance of 57 ± 6 pc from the SMBH. For the first time, we calculate spatially resolved gas evacuation timescales for the cold molecular gas reservoirs ostensibly sourcing the outflows, and find that gas evacuating to ∼400 pc from the SMBH occurs on timescales of 10 ^6.0 –10 ^7.6 yr. These results indicate that the multiphase active galactic nucleus (AGN) outflows are effective in clearing the inner few hundred parsecs of NGC 3227’s gas content on timescales that may set the AGN duty cycle of 10 ⁵ –10 ⁸ yr.

JWST NIRCam and MIRI photometry of NGC 602, a low-metallicity young star cluster in the Small Magellanic Cloud, reveals an extended mid-infrared bright emission feature designated as MZS-1. This feature is prominent between 10 and 25.5 μm, but is extremely faint at 7.7 μm and entirely undetected at shorter wavelengths. MZS-1 exhibits an elliptical morphology with a major axis of approximately 8″ and a minor axis of about 4″. Its elongated shape and multiple emission peaks in the two-dimensional flux map suggest a group of deeply embedded sources with blackbody-like temperatures ranging from 100 K to 140 K. Spectral energy distribution fitting using the T. P. Robitaille (2017) model grids identifies these sources as Stage I young stellar objects (YSOs) with masses below ∼3 M _⊙ and total stellar mass of the protocluster ≈∼300 M _⊙ (based on Salpeter IMF). The low YSO masses are consistent with their absence in Spitzer-based catalogs due to sensitivity limits. By revealing a deeply embedded, low-mass protocluster invisible in previous surveys, this work highlights JWST’s unparalleled resolution and sensitivity in uncovering the earliest stages of low-mass cluster formation in the metal-poor regime.

JWST NIRCam and MIRI photometry of NGC 602, a low-metallicity young star cluster in the Small Magellanic Cloud, reveals an extended mid-infrared bright emission feature designated as MZS-1. This feature is prominent between 10 and 25.5 microns, but is extremely faint at 7.7 microns and entirely undetected at shorter wavelengths. MZS-1 exhibits an elliptical morphology with a major axis of approximately 8 arcseconds and a minor axis of about 4 arcseconds. Its elongated shape and multiple emission peaks in the two-dimensional flux map suggest a group of deeply embedded sources with blackbody-like temperatures ranging from 100 K to 140 K. SED fitting using the Robitaille 2017 model grids identifies these sources as Stage I young stellar objects (YSOs) with masses below approximately 3 solar masses and a total stellar mass of the protocluster of about 300 solar masses (based on a Salpeter IMF). The low YSO masses are consistent with their absence in Spitzer-based catalogs due to sensitivity limits. By revealing a deeply embedded, low-mass protocluster invisible in previous surveys, this work highlights JWST's unparalleled resolution and sensitivity in uncovering the earliest stages of low-mass cluster formation in the metal-poor regime.

Active galactic nuclei (AGN) are known to drive ionized gas into their host galaxies, which may affect the evolution of both the central supermassive black holes and their hosts. In the case of NGC 3516, a nearby Seyfert 1 galaxy, these AGN winds have historically proven difficult to disentangle from galactic rotation. Using long slit spectroscopy at multiple position angles from the Hubble Space Telescope Space Telescope Imaging Spectrograph and the Apache Point Observatory Kitt Peak Ohio State Multi Object Spectrograph, we separate these kinematic components by fitting multiple Gaussians to the Hα, N II, Hβ, and O III emission lines along the slits. We present a biconical outflow model that agrees well with the observed kinematics of the outflowing gas in the narrow-line region (NLR). Our results indicate that the structure of the O III emission is explained by dusty gas spirals in the galactic disk that are illuminated by the ionizing bicone, which is viewed along one edge, resulting in the complex nuclear kinematics. Our view into the bicone edge is consistent with the multiple, deep components of ionized absorption lines seen in UV and X-ray spectra of NGC 3516. The observed turnover in the velocity of the NLR clouds matches that from a simple dynamical model of radiative acceleration by the AGN and gravitational deceleration by the AGN and galaxy, indicating they are the principal forces at work on the gas clouds. Finally, the model launch radii indicate that the outflowing clouds originate primarily from the inner dusty spirals near the AGN.

Active galactic nuclei (AGN) are known to drive ionized gas into their host galaxies, which may affect the evolution of both the central supermassive black holes and their hosts. In the case of NGC 3516, a nearby Seyfert 1 galaxy, these AGN winds have historically proven difficult to disentangle from galactic rotation. Using long-slit spectroscopy at multiple position angles from Hubble Space Telescope’s Space Telescope Imaging Spectrograph and Apache Point Observatory’s Kitt Peak Ohio State Multi-Object Spectrograph, we separate these kinematic components by fitting multiple Gaussians to the Hα, [N II], Hβ, and [O III] emission lines along the slits. We present a biconical outflow model that agrees well with the observed kinematics of the outflowing gas in the narrow-line region (NLR). Our results indicate that the structure of the [O III] emission is explained by dusty gas spirals in the galactic disk that are illuminated by the ionizing bicone, which is viewed along one edge, resulting in the complex nuclear kinematics. Our view into the bicone edge is consistent with the multiple, deep components of ionized absorption lines seen in UV and X-ray spectra of NGC 3516. The observed turnover in the velocity of the NLR clouds matches that from a simple dynamical model of radiative acceleration by the AGN and gravitational deceleration by the AGN and galaxy, indicating they are the principal forces at work on the gas clouds. Finally, the model launch radii indicate that the outflowing clouds originate primarily from the inner dusty spirals near the AGN.