Star formation in the outskirts of DDO 154: A top-light IMF in a nearly dormant disc

Adam B. Watts, Gerhardt R. Meurer, Claudia D.P. Lagos, Sarah M. Bruzzese, Pavel Kroupa, Tereza Jerabkova

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

We present optical photometry of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/Wide Field Camera (WFC) data of the resolved stellar populations in the outer disc of the dwarf irregular galaxy DDO 154. The photometry reveals that young main sequence (MS) stars are almost absent from the outermost HI disc. Instead, most are clustered near the main stellar component of the galaxy. We constrain the stellar initial mass function (IMF) by comparing the luminosity function of the MS stars to simulated stellar populations, assuming a constant star formation rate over the dynamical time-scale. The best-fitting IMF is deficient in high-mass stars compared to a canonical Kroupa IMF, with a best-fitting slope α = -2.45 and upper mass limit MU = 16M. This top-light IMF is consistent with predictions of the integrated galactic IMF theory. Combining the HST images with HI data from The HI Nearby Galaxy Survey (THINGS), we determine the star formation law (SFL) in the outer disc. The fit has a power-law exponent N = 2.92 ± 0.22 and zero-point A = 4.47 ± 0.65 × 10-7M yr-1 kpc-2. This is depressed compared to the Kennicutt- Schmidt SFL, but consistent with weak star formation observed in diffuse HI environments. Extrapolating the SFL over the outer disc implies that there could be significant star formation occurring that is not detectable in H a. Last, we determine the Toomre stability parameter Q of the outer disc of DDO 154 using the THINGS HI rotation curve and velocity dispersion map. 72 per cent of the HI in our field has Q ≤ 4 and this incorporates 96 per cent of the observed MS stars. Hence, 28 per cent of the HI in the field is largely dormant.

Original languageEnglish
Pages (from-to)5554-5567
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Volume477
Issue number4
DOIs
Publication statusPublished - 11 Jul 2018

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star formation
main sequence stars
galaxies
Hubble Space Telescope
photometry
cameras
irregular galaxies
dwarf galaxies
star formation rate
power law
luminosity
exponents
slopes
timescale
stars
curves
prediction
predictions

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Watts, Adam B. ; Meurer, Gerhardt R. ; Lagos, Claudia D.P. ; Bruzzese, Sarah M. ; Kroupa, Pavel ; Jerabkova, Tereza. / Star formation in the outskirts of DDO 154 : A top-light IMF in a nearly dormant disc. In: Monthly Notices of the Royal Astronomical Society. 2018 ; Vol. 477, No. 4. pp. 5554-5567.
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title = "Star formation in the outskirts of DDO 154: A top-light IMF in a nearly dormant disc",
abstract = "We present optical photometry of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/Wide Field Camera (WFC) data of the resolved stellar populations in the outer disc of the dwarf irregular galaxy DDO 154. The photometry reveals that young main sequence (MS) stars are almost absent from the outermost HI disc. Instead, most are clustered near the main stellar component of the galaxy. We constrain the stellar initial mass function (IMF) by comparing the luminosity function of the MS stars to simulated stellar populations, assuming a constant star formation rate over the dynamical time-scale. The best-fitting IMF is deficient in high-mass stars compared to a canonical Kroupa IMF, with a best-fitting slope α = -2.45 and upper mass limit MU = 16M⊙. This top-light IMF is consistent with predictions of the integrated galactic IMF theory. Combining the HST images with HI data from The HI Nearby Galaxy Survey (THINGS), we determine the star formation law (SFL) in the outer disc. The fit has a power-law exponent N = 2.92 ± 0.22 and zero-point A = 4.47 ± 0.65 × 10-7M⊙ yr-1 kpc-2. This is depressed compared to the Kennicutt- Schmidt SFL, but consistent with weak star formation observed in diffuse HI environments. Extrapolating the SFL over the outer disc implies that there could be significant star formation occurring that is not detectable in H a. Last, we determine the Toomre stability parameter Q of the outer disc of DDO 154 using the THINGS HI rotation curve and velocity dispersion map. 72 per cent of the HI in our field has Q ≤ 4 and this incorporates 96 per cent of the observed MS stars. Hence, 28 per cent of the HI in the field is largely dormant.",
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Star formation in the outskirts of DDO 154 : A top-light IMF in a nearly dormant disc. / Watts, Adam B.; Meurer, Gerhardt R.; Lagos, Claudia D.P.; Bruzzese, Sarah M.; Kroupa, Pavel; Jerabkova, Tereza.

In: Monthly Notices of the Royal Astronomical Society, Vol. 477, No. 4, 11.07.2018, p. 5554-5567.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Star formation in the outskirts of DDO 154

T2 - A top-light IMF in a nearly dormant disc

AU - Watts, Adam B.

AU - Meurer, Gerhardt R.

AU - Lagos, Claudia D.P.

AU - Bruzzese, Sarah M.

AU - Kroupa, Pavel

AU - Jerabkova, Tereza

PY - 2018/7/11

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N2 - We present optical photometry of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/Wide Field Camera (WFC) data of the resolved stellar populations in the outer disc of the dwarf irregular galaxy DDO 154. The photometry reveals that young main sequence (MS) stars are almost absent from the outermost HI disc. Instead, most are clustered near the main stellar component of the galaxy. We constrain the stellar initial mass function (IMF) by comparing the luminosity function of the MS stars to simulated stellar populations, assuming a constant star formation rate over the dynamical time-scale. The best-fitting IMF is deficient in high-mass stars compared to a canonical Kroupa IMF, with a best-fitting slope α = -2.45 and upper mass limit MU = 16M⊙. This top-light IMF is consistent with predictions of the integrated galactic IMF theory. Combining the HST images with HI data from The HI Nearby Galaxy Survey (THINGS), we determine the star formation law (SFL) in the outer disc. The fit has a power-law exponent N = 2.92 ± 0.22 and zero-point A = 4.47 ± 0.65 × 10-7M⊙ yr-1 kpc-2. This is depressed compared to the Kennicutt- Schmidt SFL, but consistent with weak star formation observed in diffuse HI environments. Extrapolating the SFL over the outer disc implies that there could be significant star formation occurring that is not detectable in H a. Last, we determine the Toomre stability parameter Q of the outer disc of DDO 154 using the THINGS HI rotation curve and velocity dispersion map. 72 per cent of the HI in our field has Q ≤ 4 and this incorporates 96 per cent of the observed MS stars. Hence, 28 per cent of the HI in the field is largely dormant.

AB - We present optical photometry of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/Wide Field Camera (WFC) data of the resolved stellar populations in the outer disc of the dwarf irregular galaxy DDO 154. The photometry reveals that young main sequence (MS) stars are almost absent from the outermost HI disc. Instead, most are clustered near the main stellar component of the galaxy. We constrain the stellar initial mass function (IMF) by comparing the luminosity function of the MS stars to simulated stellar populations, assuming a constant star formation rate over the dynamical time-scale. The best-fitting IMF is deficient in high-mass stars compared to a canonical Kroupa IMF, with a best-fitting slope α = -2.45 and upper mass limit MU = 16M⊙. This top-light IMF is consistent with predictions of the integrated galactic IMF theory. Combining the HST images with HI data from The HI Nearby Galaxy Survey (THINGS), we determine the star formation law (SFL) in the outer disc. The fit has a power-law exponent N = 2.92 ± 0.22 and zero-point A = 4.47 ± 0.65 × 10-7M⊙ yr-1 kpc-2. This is depressed compared to the Kennicutt- Schmidt SFL, but consistent with weak star formation observed in diffuse HI environments. Extrapolating the SFL over the outer disc implies that there could be significant star formation occurring that is not detectable in H a. Last, we determine the Toomre stability parameter Q of the outer disc of DDO 154 using the THINGS HI rotation curve and velocity dispersion map. 72 per cent of the HI in our field has Q ≤ 4 and this incorporates 96 per cent of the observed MS stars. Hence, 28 per cent of the HI in the field is largely dormant.

KW - Galaxies: dwarf

KW - Galaxies: individual (DDO 154)

KW - Galaxies: stellar content

KW - Mass function

KW - Stars: luminosity function

KW - Stars: massive

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U2 - 10.1093/mnras/sty1006

DO - 10.1093/mnras/sty1006

M3 - Article

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SP - 5554

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JF - Monthly Notices of the Royal Astronomical Society

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