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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Comparison of stellar populations in simulated and real post-starburst galaxies in MaNGA

ABSTRACT Recent integral field spectroscopic (IFS) surveys have revealed radial gradients in the optical spectral indices of post-starburst (PSB) galaxies, which can be used to constrain their formation histories. We study the spectral indices of post-processed mock IFS datacubes of binary merger simulations, carefully matched to the properties of the MaNGA IFS survey, with a variety of black hole (BH) feedback models, progenitor galaxies, orbits, and mass ratios. Based on our simulation sample, we find that only major mergers on prograde–prograde or retrograde–prograde orbits in combination with a mechanical BH feedback model can form galaxies with weak enough ongoing star formation, and therefore absent H α emission, to be selected by traditional PSB selection methods. We find strong fluctuations in nebular emission line strengths, even within the PSB phase, suggesting that H α selected PSBs are only a subsample of the underlying population. The global PSB population can be more robustly identified using stellar continuum-based approaches. The difficulty in reproducing the very young PSBs in simulations potentially indicates that new sub-resolution star formation recipes are required to properly model the process of star formation quenching. In our simulations, we find that the starburst peaks at the same time at all radii, but is stronger and more prolonged in the inner regions. This results in a strong time evolution in the radial gradients of the spectral indices that can be used to estimate the age of the starburst without reliance on detailed star formation histories from spectral synthesis models.

Zheng, Yirui↗
DOE OSTI2022

SDSS-IV MaNGA: Understanding Ionized Gas Turbulence Using Integral Field Spectroscopy of 4500 Star-forming Disk Galaxies

The Sloan Digital Sky Survey MaNGA program has now obtained integral field spectroscopy for over 10,000 galaxies in the nearby universe. We use the final MaNGA data release DR17 to study the correlation between ionized gas velocity dispersion and galactic star formation rate, finding a tight correlation in which σ Hα from galactic H ιι regions increases significantly from ~18–30 km s –1 , broadly in keeping with previous studies. In contrast, σ Hα from diffuse ionized gas increases more rapidly from 20–60 km s –1 . Using the statistical power of MaNGA, we investigate these correlations in greater detail using multiple emission lines and determine that the observed correlation of σ Hα with local star formation rate surface density is driven primarily by the global relation of increasing velocity dispersion at higher total star formation rate, as are apparent correlations with stellar mass. Assuming H ιι region models consistent with our finding that σ [O III] < σ Hα < σ [O I] , we estimate the velocity dispersion of the molecular gas in which the individual H ιι regions are embedded, finding values σ Mol = 5–30 km s –1 consistent with ALMA observations in a similar mass range. Finally, we use variations in the relation with inclination and disk azimuthal angle to constrain the velocity dispersion ellipsoid of the ionized gas σ z /σ r = 0.84 ± 0.03 and σ Φ /σ r = 0.91 ± 0.03, similar to that of young stars in the Galactic disk. Our results are most consistent with the theoretical models in which turbulence in modern galactic disks is driven primarily by star formation feedback.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Stellar density enhancements associated with IRAS sources in L1641

We obtained H and K' images of 59 Infrared Astronomical Satellite (IRAS) sources associated with dense molecular gas in L1641. Some of the sources were also imaged in narrow-band L and M. Using these near-IR images and photometry, we are able to identify the near-IR counterparts for most of the IRAS sources. The spectral energy distributions of the sources suggest that all of them are young stellar objects (class I and II sources). Most importantly, we find in this study that 14 IRAS sources are associated with small (but statistically significant) groupings of bright near-IR sources defined as stellar density enhancements (SDEs). The spatial distribution of young stars in the Orion A molecular cloud can be characterized by a range of stellar densities, from the Trapezium Cluster, to the SDEs, to individual stars. We conjecture that the SDEs are regions of continuous star formation within or around dense molecular cores and that they may represent an important mode of star formation in L1641. If true, adjustments to the standard star formation model may be required.

Chen, Hua↗
NASA NTRS1990

The distribution of warm ionized gas in NGC 891

Narrow-band imaging is presented of the edge-on spiral NGC 891 in the H-alpha and S II 6716, 6731 A forbidden lines. Emission from H II regions confined to the plane of the galaxy and from diffuse gas up to about 4 kpc off the plane is readily detected. The full radial extent of the diffuse emission in the plane is about 30 kpc. NGC 891 is found to have a surface density of diffuse ionized gas twice the Galactic value, a thicker ionized gas layer, and a larger surface density of ionized gas relative to neutral gas. These are interpreted as consequences of a relatively high level of star formation in this galaxy. Other star formation tracers indicate the same conclusion. Many vertical H-alpha filaments, or 'worms,' extending to over 2 kpc off the plane of the galaxy are seen. These worms are interpreted in terms of chimney models for the interstellar media of spirals.

Rand, Richard J.↗
NASA NTRS1993

NGC 5018 - A metal-poor giant elliptical

Far-UV observations are presently used to investigate the origin of the weak Mg2 index in the spectrum of NGC 5018; IUE spectra are obtained for the central regions of the galaxy, in order to detect evidence of ongoing star formation. It is concluded that star formation cannot produce the weak-lined spectrum in question, and that NGC 5018 seems to be a giant elliptical galaxy with the mean metallicity of a dwarf elliptical, representing a class of ellipticals that strongly deviates from the log sigma-Mg2 relationship due to intrinsic differences in their old stellar populations.

Bertola, Francesco↗
DOE OSTI2021

Eridanus II: A Fossil from Reionization with an Off-center Star Cluster

In this work, we present deep Hubble Space Telescope (HST) photometry of the ultra-faint dwarf galaxy Eridanus II (Eri II). Eri II, which has an absolute magnitude of M V = -7.1, is located at a distance of 339 kpc, just beyond the virial radius of the Milky Way. We determine the star formation history of Eri II and measure the structure of the galaxy and its star cluster. We find that a star formation history consisting of two bursts, constrained to match the spectroscopic metallicity distribution of the galaxy, accurately describes the Eri II stellar population. The best-fit model implies a rapid truncation of star formation at early times, with >80% of the stellar mass in place before z ~ 6. A small fraction of the stars could be as young as 8 Gyr, but this population is not statistically significant; Monte Carlo simulations recover a component younger than 9 Gyr only 15% of the time, where they represent an average of 7 ± 4% of the population. These results are consistent with theoretical expectations for quenching by reionization. The HST depth and angular resolution enable us to show that Eri II’s cluster is offset from the center of the galaxy by a projected distance of 23 ± 3 pc. This offset could be an indication of a small (~50–75 pc) dark matter core in Eri II. Moreover, we demonstrate that the cluster has a high ellipticity of and is aligned with the orientation of Eri II within 3° ± 6°, likely due to tides. The stellar population of the cluster is indistinguishable from that of Eri II itself.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Stellar Content of H72.97-69.39, a Potential Super Star Cluster in the Making

Young massive clusters and super star clusters (SSCs) represent an extreme mode of star formation. Far-infrared imaging of the Magellanic Clouds has identified one potential embedded SSC, HSO BMHERICC J72.971176-69.391112 (H72.97-69.39 in short), in the southwest outskirts of the Large Magellanic Cloud. We present Gemini Flamingos 2 and GSAOI near-infrared imaging of a 3′ × 3′ region around H72.97-69.39 in order to characterize the stellar content of the cluster. The stellar content is probed down to 1.5 M {sub ⊙}. We find substantial dust extinction across the cluster region, extending up to A {sub K} of 3. Deeply embedded stars are associated with ALMA-detected molecular gas suggesting that star formation is ongoing. The high spatial resolution of the GSAOI data allows identification of the central massive object associated with the {sup 13}CO ALMA observations and detection of fainter low-mass stars around the H30α ALMA source. The morphology of the molecular gas and the nebulosity from adjacent star formation suggest they have interacted covering a region of several parsecs. The total stellar content in the cluster is estimated from the intermediate- and high-mass stellar content to be at least 10,000 M {sub ⊙}, less than R136 with up to 100,000 M {sub ⊙} within 4.7 pc radius, but places it in the regime of an SSC. Based on the extinction determination of individual stars we estimate a molecular gas mass in the vicinity of H72.97-69.39 of 6600 M {sub ⊙}, suggesting more star formation can be expected.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Stellar populations with MEGARA: The inner regions of NGC 7025

This paper aims to determine the capabilities of the MEGARA spectrograph at the Gran Telescopio Canarias (GTC), which is an optical integral-field unit, for studying stellar populations. We also aim to exploit its combination of high spectral (R ~ 6000, 12 000 and 20 000) and spatial (0.62") resolution within its 12".5 × 11"​​.3 field of view. We do this by analysing the commissioning data of the nearby S0a galaxy NGC 7025. We establish a systematic method through which we can determine the properties of the stellar populations in the observations made with MEGARA, more specifically, within the MEGADES legacy project. For this paper in particular, we determine the properties of the stellar populations of NGC 7025. We used MEGARA observations of galaxy NGC 7025 that were taken during the commissioning phase of the instrument. We applied different approaches to estimate the properties of the stellar populations with the highest possible certainty. In addition to the specific study of NGC 7025 and in the context of the MEGADES survey, we have carried out a number of tests to determine the expected errors (including potential biases) in these star formation history (SFH) derivations as a function of these parameters, namely spectral setup, signal-to-noise ratio, σ, and the SFH itself. All the studies we conduct (both full spectral fitting and absorption line indices) of the stellar populations of NGC 7025 indicate that the stars that form its bulge have supersolar metallicity and considerably old ages (~10 Gyr) in general. Using three different combinations of MEGARA spectral setups, we determined that the bulge of NGC 7025 has smild negative mass-weighted age gradient. For the more detailed SFH, our results indicate that in addition to a rather constant star formation at early epochs, a peak in the formation history of the stars in the bulge is also found 3.5–4.5 Gyr ago. This partly explains the mass-weighted age gradients we measured. The scenario presented in NGC 7025 is that of an isolated galaxy under secular evolution that about 3.5–4.5 Gyr ago likely experienced a minor merger (mass ratio 1/10) that induced an increase in star formation and also perturbed the morphology of its outer disc. In addition to these specific results for NGC 7025, we report different lessons learned for the ongoing exploitation of the MEGADES survey with the GTC, such as the need to obtain combined observations in the LR-B + LR-V setups and a signal-to-noise ratio of at least 20 per Å.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Are Milky-Way-like galaxies like the Milky Way? A view from SDSS-IV/MaNGA

ABSTRACT In this paper, we place the Milky Way (MW) in the context of similar-looking galaxies in terms of their star-formation and chemical evolution histories. We select a sample of 138 Milky Way analogues (MWAs) from the SDSS-IV/MaNGA survey based on their masses, Hubble types, and bulge-to-total ratios. To compare their chemical properties to the detailed spatially-resolved information available for the MW, we use a semi-analytic spectral fitting approach, which fits a self-consistent chemical-evolution and star-formation model directly to the MaNGA spectra. We model the galaxies’ inner and outer regions assuming that some of the material lost in stellar winds falls inwards. We also incorporate chemical enrichment from type II and Ia supernovae to follow the alpha-element abundance at different metallicities and locations. We find some MWAs where the stellar properties closely reproduce the distribution of age, metallicity, and alpha enhancement at both small and large radii in the MW. In these systems, the match is driven by the longer time-scale for star formation in the outer parts, and the inflow of enriched material to the central parts. However, other MWAs have very different histories. These divide into two categories: self-similar galaxies where the inner and outer parts evolve identically; and centrally-quenched galaxies where there is very little evidence of late-time central star formation driven by material accreted from the outer regions. We find that, although selected to be comparable, there are subtle morphological differences between galaxies in these different classes, and that the centrally-quenched galaxies formed their stars systematically earlier.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Interstellar gas and dust in the young cluster IC 348

We have completed a multiband absorption- and emission-line study of a star embedded in the young cluster IC 348, to determine the environmental effect of star formation on the interstellar medium (ISM) local to the region. The hottest and youngest star in IC 348 is BD +31 deg 643, a B5 V star which samples the inner bright nebular region. The nearby star omicron Per, which lies only 8 min to the north and is thought to lie beyond IC 348, samples the gas and dust which has not been processed by very recent star formation. We speculate that the ISM throughout the region was originally the same as that currently seen toward omicron Per, but now the constrasting environmental conditions due to the recent star formation have led to marked differences in the atomic, molecular, and dust characteristics of IC 348. These contrasts include what we have termed a 'composite' UV extinction curve for BD +31 deg 643, evidence for enhanced density and enhanced depletions within IC 348 and very different molecular abundances in the interstellar sightline to BD +31 deg 643. Toward BD +31 deg 643, we find a higher column density of CH, but lower CN and very much higher CH(+) than measured toward omicron Per. We conclude that the physical and chemical state of the gas and dust has been altered by local processes and conditions within IC 348. The characteristics of the ISM in IC 348, via our study of the star BD +31 deg 643, closely resembles those seen toward rho Oph, another sight line passing through a bright nebular region. However, the stars are not as hot in IC 348 as in Ophiuchus, so their effect on the local ISM is not as severe.

Snow, Theodore P.↗
NASA NTRS1987

Formation and heating of molecular cloud cores

The origin of molecular cloud cores and their evolution into star-forming regions are discussed, reviewing the results of recent theoretical investigations. Numerical results are presented graphically, and it is argued that the existence and properties of self-gravitating clouds can be explained most easily by the action of magnetic fields. Supercritical and subcritical cloud regimes (where the cloud mass is greater or less, respectively, than the mass at which cloud self-gravity can overcome magnetic-field support) are defined and related to two types of star formation: (1) highly efficient star formation and (2) inefficient formation of low-mass stars. Mechanism (1) is shown to favor the formation of high-mass stars whenever significant core heating occurs (e.g., via ambipolar diffusion).

Lizano, Susana↗
DOE OSTI2021

An IFU View of the Active Galactic Nuclei in MaNGA Galaxy Pairs

The role of active galactic nuclei (AGNs) during galaxy interactions and how they influence the star formation in the system are still under debate. We use a sample of 1156 galaxies in galaxy pairs or mergers (hereafter "pairs") from the MaNGA survey. This pair sample is selected by the velocity offset, projected separation, and morphology, and is further classified into four cases along the merger sequence based on morphological signatures. We then identify a total of 61 (5.5%) AGNs in pairs based on the emission-line diagnostics. No evolution of the AGN fraction is found, either along the merger sequence or compared to isolated galaxies (5.0%). We observe a higher fraction of passive galaxies in galaxy pairs, especially in the pre-merging cases, and associate the higher fraction to their environmental dependence. The isolated AGN and AGNs in pairs show similar distributions in their global stellar mass, star-formation rate (SFR), and central [O iii] surface brightness. AGNs in pairs show radial profiles of increasing specific SFR and declining Dn4000 from center to outskirts, and no significant difference from the isolated AGNs. This is clearly different from star-forming galaxies (SFGs) in our pair sample, which show enhanced central star formation, as reported before. AGNs in pairs have lower Balmer decrements at outer regions, possibly indicating less dust attenuation. Our findings suggest that AGNs are likely follow an inside-out quenching and the merger impact on the star formation in AGNs is less prominent than in SFGs.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2009

A Smoking Gun in the Carina Nebula

The Carina Nebula is one of thc youngest, most active sites of massive star formation in our Galaxy. In this nebula, we have discovered a bright X-ray source that has persisted for approx.30 years. The soft X-ray spectrum. consistent with kT approx.130 eV blackbody radiation with mild extinction, and no counterpart in the near- and mid-infrared wavelengths indicate that it is a, approx. 10(exp 6)-year-old neutron star housed in the Carina Nebula. Current star formation theory does not suggest that the progenitor of the neutron star and massive stars in the Carina Nebula, in particular (eta)Car, are coeval. This result demonstrates that the Carina Nebula experienced at least two major episodes of massive star formation. The neutron star would be responsible for remnants of high energy activity seen in multiple wavelengths.

Hamaguchi, Kenji↗
NASA NTRS1995

The detection of molecular gas in the ring galaxy Arp 143

We have used the NRAO 12 m telescope to map the inner 10 kpc of NGC 2445, the ring galaxy in Arp 143, in CO-12(J = 1-0). Emission is peaked near the ring galaxy nucleus, but we find evidence for an additional asymmetric and extended CO component. This extended CO distribution is consistent with an approximately 8 kpc diameter crescent-shaped ring of molecular gas, similar to the one seen in H I, accounting for approximately half of the total CO flux. Assuming this distribution, we derive a total H2 mass for NGC 2445 of 0.4-2.4 x 10(exp 10) solar mass, depending on whether a Galactic or low-metallicity Large Magellanic Cloud (LMC) conversion factor is used, and an H2/H I mass ratio between 0.9 and 5. The ring is experiencing low rates of massive star formation despite very high gas column densities. We find that the gas surface density exceeds the critical threshold for star formation throughout the ring, even without a possible contribution from a significant molecular component. The absence of vigorous star formation is most simply understood in terms of its youth (approximately 30 Myr): massive stars have not had time to form in large numbers. Our results support the interpretation that NGC 2445 is a nascent ring galaxy, seen prior to its ring starburst phase.

Higdon, James L.↗
NASA NTRS2019

Spatially Resolved Outflows in a Seyfert Galaxy at z=2.39

We present the first spatially resolved analysis of rest-frame optical and UV (UltraViolet) imaging and spectroscopy for a lensed galaxy at z equals 2.39 hosting a Seyfert active galactic nucleus (AGN). Proximity to a natural guide star has enabled observations with high signal-to-noise ratio using Very Large Telescope SINFONI (Spectrograph for INtegral Field Observations in the Near Infrared) plus adaptive optics (AO) of rest-frame optical diagnostic emission lines, which exhibit an underlying broad component with full width at half maximum approximately 700 kilometers per second in both the Balmer and forbidden lines. Measured line ratios place the outflow robustly in the region of the ionization diagnostic diagrams associated with AGNs. This unique opportunity - combining gravitational lensing, AO guiding, redshift, and AGN activity - allows for a magnified view of two main tracers of the physical conditions and structure of the interstellar medium in a star-forming galaxy hosting a weak AGN at Cosmic Noon. By analyzing the spatial extent and morphology of the Lyman alpha spectral line and dust-corrected Hydrogen spectral line emission, disentangling the effects of star formation and AGN ionization on each tracer, and comparing the AGN-induced mass outflow rate to the host star formation rate, we find that the AGN does not significantly impact the star formation within its host galaxy.

Fischer, Travis C.↗
DOE OSTI2021

A study of outer disc stellar populations of face-on star-forming galaxies in SDSS-IV MaNGA: causes of H α deficiency

ABSTRACT Integral field unit spectra of face-on star-forming galaxies from the MaNGA survey are stacked in radial bins so as to reach an S/N high enough to measure emission lines and Lick indices out to 2.5–3Re. Two-thirds of galaxies have stellar populations in the outer discs that are older, more metal poor, and less dusty than in the inner discs. Recent bursts of star formation have occurred more frequently in the outer disc, but extinction-corrected H α equivalent widths are significantly lower at fixed Dn(4000) in these regions. I examine the properties of a subset of galaxies with the most H α-deficient outer discs. These regions contain young stellar populations that must have formed within the last 0.5 Gyr, but have extinction-corrected H α values well below the values predicted for a standard Kroupa initial mass function. The H α-deficient galaxies have flat Dn(4000) and H δA profiles with little radial fluctuation, indicating that star formation has occurred extremely uniformly across the entire disc. The H α line profiles indicate that the ionized gas kinematics is also very regular across the disc. The main clue to the origin of the H α deficiency is that it sets in at the same radius where the dust extinction abruptly decreases, suggesting a mode of star formation deficient in massive stars in quiescent, H i-dominated gas. Finally, I have carried out a search for galaxies with signatures of unusual H α kinematics and find that 15 per cent of the sample exhibits evidence for significant ionized gas that is displaced from the systemic velocity of the disc.

79 ASTRONOMY AND ASTROPHYSICS↗