Theory of the Star Formation Rate

AbstractThis work presents a new physical model of the star formation rate (SFR), tested with a large set of numerical simulations of driven, supersonic, self-gravitating, magneto-hydrodynamic (MHD) turbulence, where collapsing cores are captured with accreting sink particles. The model depends on the relative importance of gravitational, turbulent, magnetic, and thermal energies, expressed through the virial parameter, αvir, the rms sonic Mach number, S,0, and the ratio of mean gas pressure to mean magnetic pressure, β0. The SFR is predicted to decrease with increasing αvir (stronger turbulence relative to gravity), and to depend weakly on S,0 and β0, for values typical of star forming regions (S,0≈4-20 and β0≈1-20). The star-formation simulations used to test the model result in an approximately constant SFR, after an initial transient phase. Both the value of the SFR and its dependence on the virial parameter found in the simulations agree very well with the theoretical predictions.

Download Full-text

A cautionary tale of attenuation in star-forming regions

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa919 ◽

2020 ◽

Vol 494 (4) ◽

pp. 4751-4770 ◽

Cited By ~ 2

Author(s):

Mallory Molina ◽

Nikhil Ajgaonkar ◽

Renbin Yan ◽

Robin Ciardullo ◽

Caryl Gronwall ◽

...

Keyword(s):

Star Formation ◽

Emission Line ◽

Star Formation Rate ◽

Formation Rate ◽

Dust Content ◽

Physical Parameters ◽

Star Forming ◽

Total Dust ◽

Star Forming Regions ◽

Field Unit

ABSTRACT The attenuation of light from star-forming galaxies is correlated with a multitude of physical parameters including star formation rate, metallicity and total dust content. This variation in attenuation is even more evident on kiloparsec scales, which is the relevant size for many current spectroscopic integral field unit surveys. To understand the cause of this variation, we present and analyse Swift/UVOT near-UV (NUV) images and SDSS/MaNGA emission-line maps of 29 nearby (z < 0.084) star-forming galaxies. We resolve kiloparsec-sized star-forming regions within the galaxies and compare their optical nebular attenuation (i.e. the Balmer emission line optical depth, $\tau ^{l}_{B}\equiv \tau _{\textrm {H}\beta }-\tau _{\textrm {H}\alpha }$) and NUV stellar continuum attenuation (via the NUV power-law index, β) to the attenuation law described by Battisti et al. We show the data agree with that model, albeit with significant scatter. We explore the dependence of the scatter of the β–$\tau ^{l}_{B}$ measurements from the star-forming regions on different physical parameters, including distance from the nucleus, star formation rate and total dust content. Finally, we compare the measured $\tau ^{l}_{B}$ and β values for the individual star-forming regions with those of the integrated galaxy light. We find a strong variation in β between the kiloparsec scale and the larger galaxy scale that is not seen in $\tau ^{l}_{B}$. We conclude that the sightline dependence of UV attenuation and the reddening of β due to the light from older stellar populations could contribute to the scatter in the β–$\tau ^{l}_{B}$ relation.

Download Full-text

Modes of star formation from Herschel

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313000537 ◽

2012 ◽

Vol 8 (S292) ◽

pp. 87-90

Author(s):

L. Testi ◽

E. Bressert ◽

S. Longmore

Keyword(s):

Star Formation ◽

Star Formation Rate ◽

Formation Rate ◽

Mass Function ◽

Initial Mass Function ◽

Dense Gas ◽

Nearby Star ◽

Star Forming ◽

Star Forming Regions ◽

Massive Cluster

AbstractWe summarize some of the results obtained from Herschel surveys of nearby star forming regions and the Galactic plane. We show that in the nearby star forming regions the starless core spatial surface density distribution is very similar to that of the young stellar objects. This, taken together with the similarity between the core mass function and the initial mass function for stars and the relationship between the amount of dense gas and star formation rate, suggest that the cloud fragmentation process defines the global outcome of star formation. This “simple” view of star formation may not hold on all scales. In particular dynamical interactions are expected to become important at the conditions required to form young massive clusters. We describe the successes of a simple criterion to identify young massive cluster precursors in our Galaxy based on (sub-)millimeter wide area surveys. We further show that in the location of our Galaxy where the best candidate for a precursor of a young massive cluster is found, the “simple” scaling relationship between dense gas and star formation rate appear to break down. We suggest that in regions where the conditions approach those of the central molecular zone of our Galaxy it may be necessary to revise the scaling laws for star formation.

Download Full-text

Star Formation in the Local Milky Way

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315005955 ◽

2015 ◽

Vol 10 (S314) ◽

pp. 8-15

Author(s):

Charles J. Lada

Keyword(s):

Star Formation ◽

Molecular Clouds ◽

Milky Way ◽

Star Formation Rate ◽

Formation Rate ◽

Young Stars ◽

Molecular Gas ◽

Physical Processes ◽

Star Forming ◽

Star Forming Regions

AbstractStudies of molecular clouds and young stars near the sun have provided invaluable insights into the process of star formation. Indeed, much of our physical understanding of this topic has been derived from such studies. Perhaps the two most fundamental problems confronting star formation research today are: 1) determining the origin of stellar mass and 2) deciphering the nature of the physical processes that control the star formation rate in molecular gas. As I will briefly outline here, observations and studies of local star forming regions are making particularly significant contributions toward the solution of both these important problems.

Download Full-text

The dense galactic environments of the Milky Way

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319003028 ◽

2018 ◽

Vol 14 (S345) ◽

pp. 34-38

Author(s):

Quang Nguyen-Luong ◽

Neal Evans ◽

Kee-Tae Kim ◽

Hyunwoo Kang ◽

Keyword(s):

Star Formation ◽

Gas Phase ◽

Massive Star ◽

Milky Way ◽

Star Formation Rate ◽

Formation Rate ◽

Dense Gas ◽

Star Forming ◽

Star Forming Regions ◽

Rate Relation

AbstractStar formation takes place in the dense gas phase, and therefore a simple dense gas and star formation rate relation has been proposed. With the advent of multi-beam receivers, new observations show that the deviation from linear relations is possible. In addition, different dense gas tracers might also change significantly the measurement of dense gas mass and subsequently the relation between star formation rate and dense gas mass. We report the preliminary results the DEnse GAs in MAssive star-forming regions in the Milky Way (DEGAMA) survey that observed the dense gas toward a suite of well-characterized massive star-forming regions in the Milky Way. Using the resulting maps of HCO+ 1–0, HCN 1–0, CS 2–1, we discuss the current understanding of the dense gas phase where star formation takes place.

Download Full-text

Molecular Gas and Star Formation in the NGC 3077 Tidal Arm

Symposium - International Astronomical Union ◽

10.1017/s0074180900198262 ◽

2004 ◽

Vol 217 ◽

pp. 498-503 ◽

Cited By ~ 1

Author(s):

Fabian Walter ◽

Crystal Martin ◽

Jürgen Ott ◽

Andreas Heithausen

Keyword(s):

Star Formation ◽

Star Formation Rate ◽

Compact Star ◽

Formation Rate ◽

Molecular Gas ◽

Star Forming ◽

Star Forming Regions ◽

Interacting Systems ◽

The Given ◽

Hubble Time

We report the discovery of extended star formation in the prominent tidal arms near NGC 3077 (member of the M 81 triplet). 36 faint compact star forming regions were identified, covering an area of 4 × 6 kpc2. HII regions are only found near the southern rim of the tidal HI arm where the HI column density reaches values above 1 × 1021 cm−2. This threshold is very similar to what is found in ‘normal’ galactic environments. We derive a total star formation rate of 2.6 × 10−3M⊙ yr−1 in the tidal feature. We also present the first high-resolution observations of molecular gas in this region. The molecular gas emission can be separated into at least 5 distinct complexes most of which do not coincide with sites of star formation. The reservoir of neutral and molecular gas in the tidal arm is huge (~5 × 108M⊙); star formation may continue at the given rate for a Hubble time. We conclude that wide-spread low-level star formation may be a common phenomenon in tidal HI tails, however it will be difficult to detect in interacting systems that are further away.

Download Full-text

What drives galaxy quenching? Resolving molecular gas and star formation in the green valley

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa128 ◽

2020 ◽

Vol 498 (1) ◽

pp. L66-L71 ◽

Cited By ~ 3

Author(s):

Simcha Brownson ◽

Francesco Belfiore ◽

Roberto Maiolino ◽

Lihwai Lin ◽

Stefano Carniani

Keyword(s):

Star Formation ◽

Star Formation Rate ◽

Formation Rate ◽

Gas Content ◽

Molecular Gas ◽

Data Sets ◽

Star Forming ◽

Spatially Resolved ◽

Star Forming Regions ◽

Central Regions

ABSTRACT We study quenching in seven green valley galaxies on kpc scales by resolving their molecular gas content using 12CO(1–0) observations obtained with NOrthern Extended Millimeter Array and Atacama Large Millimeter Array, and their star formation rate using spatially resolved optical spectroscopy from the Mapping Nearby Galaxies at Apache Point Observatory survey. We perform radial stacking of both data sets to increase the sensitivity to molecular gas and star formation, thereby avoiding biases against strongly quenched regions. We find that both spatially resolved gas fraction (fgas) and star formation efficiency ($\rm {SFE}$) are responsible for quenching green valley galaxies at all radii: both quantities are suppressed with respect to typical star-forming regions. fgas and $\rm {SFE}$ have roughly equal influence in quenching the outer disc. We are, however, unable to identify the dominant mechanism in the strongly quenched central regions. We find that fgas is reduced by $\rm \sim\! 1~dex$ in the central regions, but the star formation rate is too low to be measured, leading to upper limits for the $\rm {SFE}$. Moving from the outer disc to central regions, the reduction in fgas is driven by an increasing $\rm \Sigma _{\star }$ profile rather than a decreasing $\rm \Sigma _{H_{2}}$ profile. The reduced fgas may therefore be caused by a decrease in the gas supply rather than molecular gas ejection mechanisms, such as winds driven by active galactic nuclei. We warn more generally that studies investigating fgas may be deceiving in inferring the cause of quenching, particularly in the central (bulge-dominated) regions of galaxies.

Download Full-text

Properties of galaxies with an offset between the position angles of the major kinematic and photometric axes

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936357 ◽

2020 ◽

Vol 634 ◽

pp. A26 ◽

Cited By ~ 2

Author(s):

L. S. Pilyugin ◽

E. K. Grebel ◽

I. A. Zinchenko ◽

J. M. Vílchez ◽

F. Sakhibov ◽

...

Keyword(s):

Star Formation ◽

Surface Brightness ◽

Star Formation Rate ◽

Formation Rate ◽

Velocity Fields ◽

Oxygen Abundance ◽

Star Forming ◽

Measured Position ◽

Central Oxygen ◽

Straight Lines

We derive the photometric, kinematic, and abundance characteristics of 18 star-forming MaNGA galaxies with fairly regular velocity fields and surface brightness distributions and with a large offset between the measured position angles of the major kinematic and photometric axes, ΔPA ≳ 20°. The aim is to examine if there is any other distinctive characteristic common to these galaxies. We found morphological signs of interaction in some (in 11 out of 18) but not in all galaxies. The observed velocity fields show a large variety; the maps of the isovelocities vary from an hourglass-like appearance to a set of straight lines. The position angles of the major kinematic axes of the stellar and gas rotations are close to each other. The values of the central oxygen abundance, radial abundance gradient, and star formation rate are distributed within the intervals defined by galaxies with small (no) ΔPA of similar mass. Thus, we do not find any specific characteristic common to all galaxies with large ΔPA. Instead, the properties of these galaxies are similar to those of galaxies with small (no) ΔPA. This suggests that either the reason responsible for the large ΔPA does not influence other characteristics or the galaxies with large ΔPA do not share a common origin, they can, instead, originate through different channels.

Download Full-text

Morphometry as a probe of the evolution of jellyfish galaxies: evidence of broadening in the surface brightness profiles of ram-pressure stripping candidates in the multicluster system A901/A902

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3226 ◽

2020 ◽

Vol 500 (1) ◽

pp. 40-53

Author(s):

Fernanda Roman-Oliveira ◽

Ana L Chies-Santos ◽

Fabricio Ferrari ◽

Geferson Lucatelli ◽

Bruno Rodríguez Del Pino

Keyword(s):

Star Formation ◽

Surface Brightness ◽

Quantitative Measurement ◽

Star Formation Rate ◽

Hubble Space Telescope ◽

Formation Rate ◽

Structural Evolution ◽

Star Forming ◽

Irregular Structures ◽

Ram Pressure

ABSTRACT We explore the morphometric properties of a group of 73 ram-pressure stripping candidates in the A901/A902 multicluster system, at z∼ 0.165, to characterize the morphologies and structural evolution of jellyfish galaxies. By employing a quantitative measurement of morphometric indicators with the algorithm morfometryka on Hubble Space Telescope (F606W) images of the galaxies, we present a novel morphology-based method for determining trail vectors. We study the surface brightness profiles and curvature of the candidates and compare the results obtained with two analysis packages, morfometryka and iraf/ellipse on retrieving information of the irregular structures present in the galaxies. Our morphometric analysis shows that the ram-pressure stripping candidates have peculiar concave regions in their surface brightness profiles. Therefore, these profiles are less concentrated (lower Sérsic indices) than other star-forming galaxies that do not show morphological features of ram-pressure stripping. In combination with morphometric trail vectors, this feature could both help identify galaxies undergoing ram-pressure stripping and reveal spatial variations in the star formation rate.

Download Full-text