Candidate LBV stars in galaxy NGC 7793 found via <i>HST</i> photometry + MUSE spectroscopy

Wofford, Aida; Ramírez, Vanesa; Boquien, M.; Thilker, David A.; Bruna, Lorenza Della; Adamo, Angela; Dyk, Schuyler D. Van; Herrero, A.; Kim, Hwi; Aloisi, Alessandra; Calzetti, Daniela; Chandar, Rupali; Dale, Daniel A.; Mink, S. E. de; Gallagher, John S.; Gouliermis, Dimitrios A.; Grasha, Kathryn; Grebel, Eva K.; Sacchi, Elena; Smith, Linda J.; Úbeda, Leonardo; Walterbos, R. A. M.; Hannon, Stephen; Messa, Matteo

doi:10.1093/mnras/staa290

Cited by 14 publications

(10 citation statements)

References 72 publications

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“…We used the observations of NGC 7793 obtained by LEGUS and Hα LEGUS, which are summarized in table 2 of Wofford et al (2020). NGC 7793 is a Southern SAd flocculent spiral galaxy that is part of the Sculptor group and is located at a Cepheid distance of 3.44 Mpc The panels are arranged in order of increasing A V value, which is why for the panels on the right, a larger offset between the red and blue curves can be observed.…”

Section: Ngc 7793mentioning

confidence: 99%

Synthetic photometry of OB star clusters with stochastically sampled IMFs: analysis of models and HST observations

Orozco-Duarte

Wofford

Vidal-García

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We present a pilot library of synthetic NUV, U, B, V, and I photometry of star clusters with stochastically sampled IMFs and ionized gas for initial masses, Mi = 103, 104, and 105 M⊙; t = 1, 3, 4, and 8 Myr; Z = 0.014 and Z = 0.002; and log(US) = −2 and −3. We compare the library with predictions from deterministic models and observations of isolated low-mass (<104 M⊙) star clusters with co-spatial compact H ii regions. The clusters are located in NGC 7793, one of the nearest galaxies observed as part of the HST LEGUS and Hα-LEGUS surveys. (1) For model magnitudes that only account for the stars: (a) the residual |deterministic mag - median stochastic mag| can be ≥0.5 mag, even for Mi = 105 M⊙; and (b) the largest spread in stochastic magnitudes occurs when Wolf-Rayet stars are present. (2) For Mi = 105 M⊙: (a) the median stochastic mag with gas can be >1.0 mag more luminous than the median stochastic magnitude without gas; and (b) nebular emission lines can contribute with $>50{{\ \rm per\ cent}}$ and $>30{{\ \rm per\ cent}}$ to the total emission in the V and I bands, respectively. (3) Age-dating OB-star clusters via deterministic tracks in the U-B versus V-I plane is highly uncertain at Z = 0.014 for Mi ∼ 103 M⊙ and Z = 0.002 for Mi ∼ 103–105 M⊙. (4) For low-mass clusters, the V-band extinction derived with stochastic models significantly depends on the value of log(US). (5) The youngest clusters tend to have higher extinction. (6) The majority of clusters have multi-peaked age PDFs. (7) Finally, we discuss the importance of characterizing the true variance in the number of stars per mass bin in nature.

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Section: Ngc 7793mentioning

confidence: 99%

Synthetic photometry of OB star clusters with stochastically sampled IMFs: analysis of models and HST observations

Orozco-Duarte

Wofford

Vidal-García

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…With the rise of integral field spectrographs, even with AO support (e.g., MUSE at the ESO/VLT), such analyses should be possible in all Local Group galaxies and the nearest galaxy groups. First such analyses are already appearing for galaxies in the Scultor group: NGC 300 [184] and NGC 7793 [185]. An unfortunate weakness in the currently available instrumentation are high-dispersion spectrographs fed by long-slits and IFUs, an important capability for kinematics/energetics of nebulae, which is becoming rare [186] at the intermediate and large telescopes.…”

Section: Discussionmentioning

confidence: 99%

Luminous Blue Variables

Weis

Bomans

2020

Galaxies

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Luminous Blue Variables are massive evolved stars, here we introduce this outstanding class of objects. Described are the specific characteristics, the evolutionary state and what they are connected to other phases and types of massive stars. Our current knowledge of LBVs is limited by the fact that in comparison to other stellar classes and phases only a few “true” LBVs are known. This results from the lack of a unique, fast and always reliable identification scheme for LBVs. It literally takes time to get a true classification of a LBV. In addition the short duration of the LBV phase makes it even harder to catch and identify a star as LBV. We summarize here what is known so far, give an overview of the LBV population and the list of LBV host galaxies. LBV are clearly an important and still not fully understood phase in the live of (very) massive stars, especially due to the large and time variable mass loss during the LBV phase. We like to emphasize again the problem how to clearly identify LBV and that there are more than just one type of LBVs: The giant eruption LBVs or η Car analogs and the S Dor cycle LBVs.

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“…) have identified O stars based on HST photometry. The catalogue is described in Wofford et al (2020), and consists of main sequence O stars of M > 20 M , selected in a colour-magnitude and colour-Q diagram 4 . The resulting completeness of this stellar catalogue is estimated to be about 75% at the lower mass limit of 20 M and rapidly growing to 90% at stellar masses above 25 M 5 .…”

Section: Data Descriptionmentioning

confidence: 99%

Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE

Bruna

Adamo

Boquien

et al. 2021

A&A

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Context. Feedback from massive stars affects the interstellar medium (ISM) from the immediate surroundings of the stars (parsec scales) to galactic (kiloparsec) scales. High-spatial resolution studies of H II regions are critical to investigate how this mechanism operates. Aims. We study the ionised ISM in NGC 7793 with the MUSE instrument at ESO Very Large Telescope (VLT), over a field of view (FoV) of ∼2 kpc2 and at a spatial resolution of ∼10 pc. The aim is to link the physical conditions of the ionised gas (reddening, ionisation status, abundance measurements) within the spatially resolved H II regions to the properties of the stellar populations producing Lyman continuum photons. Methods. The analysis of the MUSE dataset, which provides a map of the ionised gas and a census of Wolf Rayet stars, is complemented with a sample of young star clusters (YSCs) and O star candidates observed with the Hubble Space Telescope (HST) and of giant molecular clouds traced in CO(2–1) emission with the Atacama Large Millimeter/submillimeter Array (ALMA). We estimated the oxygen abundance using a temperature-independent strong-line method. We determined the observed total amount of ionising photons (Q(H0)) from the extinction corrected Hα luminosity. This estimate was then compared to the expected Q(H0) obtained by summing the contributions of YSCs and massive stars. The ratio of the two values gives an estimate for the escape fraction (fesc) of photons in the region of interest. We used the [S II]/[O III] ratio as a proxy for the optical depth of the gas and classified H II regions into ionisation bounded, or as featuring channels of optically thin gas. We compared the resulting ionisation structure with the computed fesc. We also investigated the dependence of fesc on the age spanned by the stellar population in each region. Results. We find a median oxygen abundance of 12 + log(O/H) ∼ 8.37, with a scatter of 0.25 dex, which is in agreement with previous estimates for our target. We furthermore observe that the abundance map of H II regions is rich in substructures, surrounding clusters and massive stars, although clear degeneracies with photoionisation are also observed. From the population synthesis analysis, we find that YSCs located in H II regions have a higher probability of being younger and less massive as well as of emitting a higher number of ionising photons than clusters in the rest of the field. Overall, we find fesc,HII = 0.67−0.12+0.08 for the population of H II regions. We also conclude that the sources of ionisation observed within the FoV are more than sufficient to explain the amount of diffuse ionised gas (DIG) observed in this region of the galaxy. We do not observe a systematic trend between the visual appearance of H II regions and fesc, pointing to the effect of 3D geometry in the small sample probed.

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Candidate LBV stars in galaxy NGC 7793 found via HST photometry + MUSE spectroscopy

Cited by 14 publications

References 72 publications

Synthetic photometry of OB star clusters with stochastically sampled IMFs: analysis of models and HST observations

Synthetic photometry of OB star clusters with stochastically sampled IMFs: analysis of models and HST observations

Luminous Blue Variables

Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE

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