5 research outputs found
Star-formation-rate estimates from water emission
(Abridged) The star-formation rate (SFR) quantitatively describes the
star-formation process in galaxies. Current ways to calibrate this rate do not
usually employ observational methods accounting for the low-mass end of stellar
populations as their signatures are too weak. Accessing the bulk of
protostellar activity within galactic star-forming regions can be achieved by
tracing signposts of ongoing star formation. One such signpost is molecular
outflows, which are bright in molecular emission. We propose to utilize the
protostellar outflow emission as a tracer of the SFR. In this work, we
introduce a novel version of the galaxy-in-a-box model, which can be used to
relate molecular emission from star formation in galaxies with the SFR. We
measured the predicted para-H2O emission at 988 GHz and corresponding SFRs for
galaxies with LFIR = - L in a distance-independent
manner, and compared them with expectations from observations. We evaluated the
derived results by varying the star formation efficiency, the free-fall time
scaling factor, and the initial mass function. For the chosen H2O transition,
relying on the current Galactic observations and star formation properties, we
are underestimating the total galactic emission, while overestimating the SFRs,
particularly for more starburst-like configurations. The current version of the
galaxy-in-a-box model accounts for a limited number of processes and
configurations, that is, it focuses on ongoing star formation in massive young
clusters in a spiral galaxy. Therefore, the inferred results, which
underestimate the emission and overestimate the SFR, are not surprising: known
sources of emission are not included in the model. To improve the results, the
next version of the model needs to include a more detailed treatment of the
entire galactic ecosystem and other processes that would contribute to the
emission.Comment: Accepted for publication in A&A. 11 pages, 6 figure
Water emission tracing active star formation from the Milky Way to high- galaxies
(Abridged) The question of how most stars in the Universe form remains open.
While star formation predominantly occurs in young massive clusters, the
current framework focuses on isolated star formation. One way to access the
bulk of protostellar activity within star-forming clusters is to trace
signposts of active star formation with emission from molecular outflows. These
outflows are bright in water emission, providing a direct observational link
between nearby and distant galaxies. We propose to utilize the knowledge of
local star formation as seen with molecular tracers to explore the nature of
star formation in the Universe. We present a large-scale statistical galactic
model of emission from galactic active star-forming regions. Our model is built
on observations of well-resolved nearby clusters. By simulating emission from
molecular outflows, which is known to scale with mass, we create a proxy that
can be used to predict the emission from clustered star formation at galactic
scales. We evaluated the impact of the most important global-star formation
parameters (i.e., initial stellar mass function (IMF), molecular cloud mass
distribution, star formation efficiency (SFE), and free-fall time efficiency)
on simulation results. We observe that for emission from the para-H2O 202 - 111
line, the IMF and molecular cloud mass distribution have a negligible impact on
the emission, both locally and globally, whereas the opposite holds for the SFE
and free-fall time efficiency. Moreover, this water transition proves to be a
low-contrast tracer of star formation. The fine-tuning of the model and
adaptation to morphologies of distant galaxies should result in realistic
predictions of observed molecular emission and make the galaxy-in-a-box model a
tool to analyze and better understand star formation throughout cosmological
times.Comment: Accepted for publication in A&A. 16 pages, 13 figure
Star-formation-rate estimates from water emission
Context. The star-formation rate (SFR) quantitatively describes the star-formation process in galaxies throughout cosmic history. Current ways to calibrate this rate do not usually employ observational methods accounting for the low-mass end of stellar populations as their signatures are too weak.
Aims. Accessing the bulk of protostellar activity within galactic star-forming regions can be achieved by tracing signposts of ongoing star formation. One such signpost is molecular outflows, which are particularly strong at the earliest stages of star formation. These outflows are bright in molecular emission, which is readily observable. We propose to utilize the protostellar outflow emission as a tracer of the SFR.
Methods. In this work, we introduce a novel version of the galaxy-in-a-box model, which can be used to relate molecular emission from star formation in galaxies with the SFR. We measured the predicted para-water emission at 988 GHz (which is particularly bright in outflows) and corresponding SFRs for galaxies with LFIR = 108 − 1011 L⊙ in a distance-independent manner, and compared them with expectations from observations.
Results. We evaluated the derived results by varying star-forming parameters, namely the star formation efficiency, the free-fall time scaling factor, and the initial mass function. We observe that for the chosen water transition, relying on the current Galactic observations and star formation properties, we are underestimating the total galactic emission, while overestimating the SFRs, particularly for more starburst-like configurations.
Conclusions. The current version of the galaxy-in-a-box model only accounts for a limited number of processes and configurations, that is, it focuses on ongoing star formation in massive young clusters in a spiral galaxy. Therefore, the inferred results, which underestimate the emission and overestimate the SFR, are not surprising: known sources of emission are not included in the model. To improve the results, the next version of the model needs to include a more detailed treatment of the entire galactic ecosystem and other processes that would contribute to the emission. Thus, the galaxy-in-a-box model is a promising step toward unveiling the star-forming properties of galaxies across cosmic time