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\input{preface}
\section{Introduction}
Turbulence is important.
Federrath, Kainulainen, Kritsuk, etc.
\section{Non-star-forming, low column-density clouds in absorption}
In \citet{Ginsburg2011a}, we noted that the \formaldehyde densitometer revealed
volume densities much higher than expected given the cloud-average densities
...
are 73 K at 6 cm and 11 K at 2 cm for the south component, and 194 K at 6 cm
and 28 K at 2 cm for the north component.
% 2001ApJ...551..747S
\FigureTwo{figures/G43.17+0.01_H2CO_overplot_gbt9x.png}
{figures/G43.16-0.03_H2CO_overplot_gbt9x.png}
{Spectra of the \formaldehyde \oneone (black), \twotwo (red), and \thirteenco
...
directly along the line of sight to W49, but additional \formaldehyde spectra
of the surrounding sources that are bright at 8-1100 \um show that they are all
at the velocity of W49 and therefore are not associated with these foreground
clouds.
Additionally, the 40 \kms cloud, known as GRSMC 43.30-0.33
\citep{Simon2001a}, was confirmed in that paper to have no associated star
formation.
The 40 \kms
cloud cloud, is observed in
its outskirts, not at the peak of the \thirteenco emission. The cloud
structure is vast, spanning $\sim0.6\degrees$, or $\sim60$ pc at $D=2.8$ kpc
\citep{Roman-Duval2009a}. It is detected in \oneone absorption at all 6
locations observed in \formaldehyde (Figure \ref{fig:40kmscloud}), but \twotwo
is only detected in front of the W49 HII region because of the higher
signal-to-noise at that location. The detected \thirteenco and \formaldehyde
lines are fairly narrow, with \formaldehyde FWHM $\sim1.3$-$2.8$ \kms and
\thirteenco widths from 1.8-5.9 \kms. The \thirteenco lines are 50\% wider
than the \formaldehyde lines.
The highest \thirteenco contours are observed as a modest IRDC, but no dust
emission peaks are observed at 500 \um or 1.1 mm. This is an indication that
...
\citep{Zeiger2010}. Nonetheless, the density is much higher than the
\thirteenco-measured cloud-average density $n\approx 400$ \percc
\citep[for cloud GRSMC\_G043.04-00.11;][]{Roman-Duval2010a}, with
$n_{\formaldehyde}/n_{\thirteenco} \approx 50$.
The discrepancy is worse using
the \citet{Simon2001a} cloud-averaged density $n\approx 100$ \percc.
Our density measurements are about 4$\times$ higher than CO/CI LVG density
measurements from \citet{Plume2004a}, though those measurements rely on
uncertain abundances and are fairly sensitive to temperature.
Since the W49 line of sight is clearly on the outskirts of the cloud, not
through its core, such a high density is unlikely to be an indication that
...
resulting \hh column densities are 3.5\ee{21} and 9.0 \ee{20} \percc
respectively. The abundances of \ortho relative to \thirteenco are 3.2\ee{-4}
and 9.8\ee{-4} respectively, or relative to \hh, 5.8\ee{-10} and 1.7\ee{-9},
which are entirely consistent with other measurements of $X_{\ortho}$.
These
are %These
%are relatively modest column densities, with $A_V=17$ and
4.5. 4.5;
%these measurements are consistent with \citet{Plume2004a} if the different
%A_V/N(H_2) conversions are corrected.
These measurements for a specific cloud validate the statistical argument made
in \citet{Ginsburg2011a}. However, upon closer inspection of the cloud
...
gravitational collapse, the free-fall times are shorter by an order of
magnitude than usually assumed. The long lifetimes of GMCs therefore implies
that the cloud cannot be undergoing gravitational collapse, but instead
maintains a turbulent equilibrium.
\todo{Strengthen this argument...}
It also demonstrates that density-based star-formation thresholds do not
independently predict star formation \citep{Parmentier2011a}. Star formation
...
% functions of column density that have recently become popular
% \citep[e.g][]{Kainulainen2009}.
\section{Implications for Turbulence}
Supersonic interstellar turbulence can be characterized by its driving mode,
Mach number $\mathcal{M}$, and magnetic field strength. The with of the turbulent density distribution
is given by
\begin{equation}
\label{eqn:sigmas}
\sigma_s^2 = \ln\left(1+b^2 \mathcal{M}^2 \frac{\beta}{\beta+1}\right)
\end{equation}
where $\beta= 2 c_s^2/v_A^2 = 2 \mathcal{M}_A^2/\mathcal{M}^2$ and $b$ ranges
from 1/3 (solenoidal, divergence-free forcing) to 1 (compressive, curl-free)
forcing. The parameter $s\equiv\rho/\rho_0$.
The observed \formaldehyde ratio depends on the \emph{mass-weighted}
probability distribution function (as opposed to the volume-weighted
distribution function, which is typically reported in simulations)
such that $p_m(s) = \rho \cdot p_s(s)$, or
\begin{equation}
\label{eqn:lognormal}
p_m(s) = \frac{s}{\sqrt{2 \pi \sigma_s^2}} \exp{\left(-\frac{(s-s_0)^2}{2 \sigma_s^2}\right)}
\end{equation}
where we have assumed a lognormal form for $p_m(s)$. Other forms of the density PDF will be
addressed in Section \ref{sec:simpdfs}.
We use LVG models of the \formaldehyde lines, which are computed assuming a
fixed local density, as a starting point to model the observations of
\formaldehyde in turbulence. Starting with a fixed \emph{mean} density, we
compute the observed \formaldehyde optical depth in both the \oneone and \twotwo
line by averaging over the mass-weighted density distribution.
\begin{equation}
\label{eqn:tauintegral}
\tau(\bar{n}) = \int_0^\infty \tau(n) p_m(n) dn
\end{equation}
where $\tau(n)$ is computed for a given density assuming a fixed
\emph{abundance} of \ortho relative to \hh, which necessarily implies a higher
column density of \ortho for the higher densities in Equation
\ref{eqn:tauintegral}. As long as the \formaldehyde lines are optically thin,
this approach should yield the right \emph{ratio} of the two lines, although the
absolute optical depths may be substantially smaller because of lower total
\ortho columns. An example of this smoothing is shown in Figure
\ref{fig:lvgsmooth}.
\Figure{figures/lognormalsmooth_density_ratio_massweight_logopr0.0_abund-9.png}
{The predicted \formaldehyde \oneone/\twotwo ratio as a function of \emph{mean}
density for a fixed abundance relative to \hh $X(\ortho) = 10^{-9}$ and \hh
ortho/para ratio 1.0. The legend shows the effect of smoothing with different
lognormal mass distributions as described in Equations \ref{eqn:sigmas} and
\ref{eqn:lognormal}. The solid line, labeled LVG, shows the predicted ratio
with no smoothing.
}
{fig:lvgsmooth}{0.5}{0}
\subsection{Turbulence and GRSMC 43.30-0.33}
Assuming a temperature $T=10$ K, consistent with both the \formaldehyde and CO
observations \citep{Plume2004a}, the sound speed in molecular gas is $c_s=0.25$
\kms. The observed line FWHM is 0.95 \kms for \formaldehyde and 1.7 \kms for
\thirteenco 1-0, so the Mach number of the turbulence is $\mathcal{M} \approx
3.8-6.8$. Assuming the thermal dominates the magnetic pressure ($\beta>>1$),
the allowed values of $\sigma_s$ range from 1.6-2.0 for $b=1$ and 1-1.3 for
$b=1/3$. If magnetic pressure is significant, the allowed values of $\sigma_s$
drop.
Given that the observed mean cloud density is $n(\hh)\sim10^2 \percc$, Figure
\ref{fig:lvgsmooth} shows that only the most extreme values of $\sigma_s$ can
explain the mean density. Even if the cloud is extremely oblate, e.g. with a
line-of-sight axis $0.1\times$ the plane-of-sky axes, $\sigma_s \gtrsim 1.5$ is
required.
These restrictions on $\sigma_s$ are strong indications that compressive
forcing must be a significant, if not dominant, mode in this molecular cloud.
If magnetic fields are in balance with or dominate thermal pressure in this
cloud \todo{Look at Crutcher's measurements of B-field with Zeeman OH
observations}, $\beta\gtrsim2/3$, the forcing must be predominantly
compressive, with $b>0.8$.
\subsection{Simulated PDFs}
\label{sec:simpdfs}
Real turbulent PDFs are not truly lognormal, though often they are
well-approximated as lognormals. We have used some of the PDFs from
\citet{Federrath2012a} to perform additional smoothing and determine
whether deviations from lognormal can explain the observed density contrasts.
To perform the smoothing, we converted the simulation's volume-weighted PDF to
a mass-weighted PDF using Equation \ref{eqn:lognormal} and used an identical
PDF shape for each mean density (i.e., we kept the shape of the PDF the same
but changed its mean for use in Equation \ref{eqn:tauintegral}). Results of this process
are shown in Figure \ref{fig:rescalepdfs}.
\FigureTwoAA{figures/federrath_pdfs_volume_mach10.png}{figures/federrath_pdfs_recentered_massweighted_fitted_mach10.png}
{PDFs from \citet{Federrath2012a}. (a) Volume-weighted PDFs for various
simulations with $\mathcal{M}=10$. (b) Mass-weighted PDFs from the same
simulations as (a). These PDFs have been recentered such that they
have a mean overdensity $s=0$.
}{fig:rescalepdfs}{1}{5in}
In order to simplify the application of these PDFs to the LVG models, we fit
the asymmetric distributions with the sum of two lognormals with different
means. This approach allows for an easier exploration of parameter space.
An example demonstrating that two lognormals is a good approximation of one of the
compressive simulations is shown in Figure \ref{fig:fittedpdf}.
\Figure{figures/federrath_mach10_rescaled_massweighted_fitted.png}
{The Mach 10 compressive simulation PDF from \citet{Federrath2012a} is shown in
blue with the best-fit single lognormal in green and sum of two lognormals in
red. The two-lognormal approximation is a good fit to the simulated PDF.}
{fig:fittedpdf}{0.5}{0}
To use these fitted two-lognormal distributions, we create new PDFs consisting
of lognormals with the sample amplitude \& width ratios and the same mean
differences as the fit in Figure \ref{fig:fittedpdf}, but with the total width
scaled. In Figure \ref{fig:compsmooth} [not included; see below], the reported widths for the
``compressive'' distributions are the widths of the wider, lower distribution
in \ref{fig:fittedpdf}.
Upon further inspection, this approximation actually does a poor job as it
fails to reproduce the tails, which are more important than the peak.
\input{solobib}
\end{document}
diff --git a/introduction.tex b/introduction.tex
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observe obscured young stars. These objects have just ignited fusion in their
cores and represent the youngest generation of new stars.
But this material has already formed stars. To see the truly cold
stuff, material, that
which still has potential to form new stars, we need to examine gas that is not
heated at all by stars. Assuming we want to look for gas that can form a star
like our sun and that the density of the gas to form is $\sim10^4$
\hh particles
per cubic centimeter (an assumption left unjustified for now), the Jeans scale
requires a temperature $T\sim10$ K, which means we need to look at wavelengths
$\lambda \gtrsim 100 \um$ in order to observe this gas.
...
the gravitational constant. More careful analyses including other factors,
e.g. external pressure on the core, yield similar values.
The Jeans
collapse instability growth time scale $\tau_{J}$ is within a factor of a few
of the free-fall collapse time $\tau_{ff}$,
$$\tau_J = \left(\frac{1}{4 \pi G \rho_0}\right)^{1/2}$$
$$\tau_{ff} = \left(\frac{3\pi}{32 G \rho_0}\right)^{1/2} = \pi\sqrt{\frac{3}{8}} \tau_J$$
implying a typical mass infall rate for an isothermal core of
diff --git a/macros.tex b/macros.tex
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\newcommand{\todo}[1]{\textcolor{red}{#1}}
\newcommand{\okinfinal}[1]{{#1}}
\newcommand{\keywords}[1]{}
\newcommand{\email}[1]{}
\newcommand{\affil}[1]{} %% only needed if not aastex
%\newcommand{\keywords}[1]{}
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%aastex hack
diff --git a/preface.tex b/preface.tex
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%\documentclass[defaultstyle,11pt]{thesis}
\documentclass[]{report} %\documentclass[]{report}
%\documentclass[]{article}
%\usepackage{aastex_hack}
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\documentclass[preprint]{aastex}
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\usepackage{latexsym} % to get LASY symbols
\usepackage{graphicx} % to insert PostScript figures
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\usepackage{multicol}
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\usepackage{url}
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diff --git a/sfnewsletter.tex b/sfnewsletter.tex
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%
%%% LaTeX MACRO FOR DISSERTATION ABSTRACTS
%%%
%%% Please use the following macro for your thesis abstract. You
%%% have one full page for everything, and you are very welcome to
%%% go into detail with your results, so the readers get a
%%% comprehensive overview of your work. Merely fill in the
%%% brackets below and mail to [email protected]. If you
%%% have problems, let me know in an accompanying note and I will fix them.
%%%
%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\documentstyle{article}
\textwidth 18cm
\textheight 23cm
\oddsidemargin -1cm
\topmargin 0cm
\parskip 0.15cm
\parindent 0pt
\small
\begin{document}
\begin{center}
%% If you use any personal Latex commands in your abstract, please include
%% their definitions here.
%% Between these brackets you write the title of your thesis:
{\Large\bf{Surveying Star Formation in the Galaxy}}
\vspace*{0.5cm}
%% Here comes your name
{\bf{ Adam Ginsburg }}
%% Here you write the institute where your thesis work was conducted, e.g.:
{Thesis work conducted at: Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, Colorado, USA}
%% Here comes your present postal address (if you are about to move and know
%% your coming address give it as well) e.g.:
{Current address:
391 UCB
Boulder, CO, USA 80309}
%% (if you use this part, remove %%)
{Address as of October 2013:
Karl-Schwarzschild-Straße 2,
85748 Garching bei München, Germany
}
%% Here comes your e-mail address:
{Electronic mail: [email protected]}
%% Name of your adviser:
{Ph.D dissertation directed by: John Bally}
%% Month and Year of thesis:
{Ph.D degree awarded: April 2013}
\vspace*{0.8cm}
\end{center}
%% Within the following brackets you place your text:
{
I studied the formation of massive stars and clusters via millimeter,
radio, and infrared observations. The Bolocam Galactic Plane Survey (BGPS)
was the first millimeter-wave blind survey of the plane of our Galaxy. I
wrote the data reduction pipeline for this survey and produced the final
publicly released data products. I ran extensive tests of the pipeline,
using simulations to probe its performance.
The BGPS detected over 8000 1.1 mm sources, the largest sample at this
wavelength ever detected. As a single-wavelength continuum survey, the
BGPS serves as a finder chart for millimeter and radio observations.
I therefore performed follow-up surveys of BGPS sources in CO 3-2 and
\formaldehyde, and others did similar follow-ups to measure velocities
and distances towards these sources.
\formaldehyde observations of ultracompact HII regions and other
millimeter-bright sources were used to measure the local molecular gas
density. These measurements hint that density within molecular clouds does
not follow a simple lognormal distribution. They also show that
star-forming clouds all contain gas at density $\gtrsim10^4$ \percc.
I used the BGPS source catalog to identify the most massive compact clumps
within the galaxy, identifying 18 with masses $M>10^4$ \msun in the first
quadrant of the Galactic plane. As these objects are all actively
star-forming, the starless timescale of massive proto-cluster clumps must
be relatively short, with lifetimes $\lesssim0.6$ Myr.
}
\end{document}
diff --git a/solobib.tex b/solobib.tex
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\ifstandalone
\bibliographystyle{apj_w_etal} % or "siam", or "alpha", or "abbrv"
\bibliography{thesis} %\bibliography{thesis} % bib database file refs.bib
\bibliography{bibdesk} % bib database file refs.bib
\fi
diff --git a/thesis.bib b/thesis.bib
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@INPROCEEDINGS{Goodman2013a,
@article{Federrath2012a,
Author = {{Federrath}, C. and {Klessen}, R.~S.},
Journal = {ArXiv e-prints},
Month = nov,
Title = {{On the Star Formation Efficiency of Turbulent Magnetized Clouds}},
Year = 2012}
@article{Plume2004a,
Author = {{Plume}, R. and {Kaufman}, M.~J. and {Neufeld}, D.~A. and {Snell}, R.~L. and {Hollenbach}, D.~J. and {Goldsmith}, P.~F. and {Howe}, J. and {Bergin}, E.~A. and {Melnick}, G.~J. and {Bensch}, F.},
Journal = {\apj},
Month = apr,
Pages = {247-258},
Title = {{Water Absorption from Line-of-Sight Clouds toward W49A}},
Volume = 605,
Year = 2004}
@article{Simon2001a,
Author = {{Simon}, R. and {Jackson}, J.~M. and {Clemens}, D.~P. and {Bania}, T.~M. and {Heyer}, M.~H.},
Journal = {\apj},
Month = apr,
Pages = {747-763},
Title = {{The Structure of Four Molecular Cloud Complexes in the BU-FCRAO Milky Way Galactic Ring Survey}},
Volume = 551,
Year = 2001}
@INPROCEEDINGS{Goodman2013a,
author = {{Goodman}, A.~A. and {Alves}, J.~F. and {Beaumont}, C. and {Benjamin}, R.~A. and
{Borkin}, M.~A. and {Burkert}, A. and {Dame}, T.~M. and {Kauffmann}, J. and
{Robitaille}, T.},
diff --git a/thesis.tex b/thesis.tex
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\usepackage{graphicx} % to insert PostScript figures
%\usepackage{deluxetable}
\usepackage{rotating} % for sideways tables/figures
\usepackage{natbib} % Requires natbib.sty, available from http://ads.harvard.edu/pubs/bibtex/astronat/
\usepackage{savesym}
...
\reader{Prof.~Jeremy Darling} % 2nd person to sign thesis
\readerThree{Prof.~Jason Glenn} % 3rd person to sign thesis
\readerFour{Prof.~Michael Shull} % 4rd person to sign thesis
\readerFour{Prof.~Neal Evans} % 4rd person to sign thesis
\readerFive{Prof.~Michael Shull} % 4rd person to sign thesis
\abstract{ \OnePageChapter % one page only ??
