1804.07306
Is the dark-matter halo spin a predictor of galaxy spin and size?
Jian, Dekel, et al
The similarity between the distributions of spins for galaxies (lambda_g) and for DM haloes (lambda_h), indicated both by simulations and observations, is naively interpreted as one-to-one correlation between the spins of a galaxy and its host halo. This is used to predict galaxy sizes in semi-analytic models via R_e ~labmda_h R_v, with R_e the halo-mass radius of the galaxy and R_v the halo radius. Utilizing two different suites of zoom-in cosmological simulations, find that lambda_g and lambda_h are in fact only barely correlated, especially at z>=1. A general smearing of the correlation is expected based on the different spin histories, where the more recently accreted baryons through streams gain and then lose significant angular momentum compared to the gradually accumulated DM. Expecting the spins of baryons and DM to be correlated at accretion into R_v, the null correlation at the end reflects an anti-correlation between lambda_g/lambda_h and lambda_h, which can partly arise from mergers and a compact SF phase that many galaxies undergo. On the other hand, the halo and galaxy spin vectors tend to be aligned, with a median cos(theta)=0.6-0.7 between galaxy and halo, consistent with in streaming within a preferred plane. The galaxy spin is better correlated with the spin of the inner halo, but this largely reflects the effect of the baryons on the halo. Following the null spin correlation, lambda_h is not a useful proxy for R_e. While the simulations reproduce a general relation of the sort R_e=AR_vir, in agreement with observational estimates, the relation becomes tighter with A=0.02(c/10)^{-0.7}, where c is the halo concentration, which in turn introduces a dependence on mass and redshift.
Special Topics
PLOS Biology
Holman, Stuart-Fox, Hauser
"Women substantially underrepresented as the last-named author in the author list, and as single authors and overrepresented as first authors relative to the overall author gender ratio. A small minority of journals bucked the overall trend and had fewer women first authors than expected, rather than more; these journals were predominantly well-known, prestigious titles such as Nature, Lance, New England Journal of Medicine, and BMJ. In most disciplines represented in our dataset, prevailing conventions regarding authorship order mean that first authors are usually early career researchers, while last authors tend to be comparatively senior. Thus, these results suggest that early career researchers are more likely to be women and senior researcher more likely to be men, relative to the overall gender ratio of the discipline in question, consistent with United States-specific survey data showing that the underrepresentation of women is highest among senior academics. In some fields, the convention is for the authors to be listed alphabetically by surname. Publications in our dataset using the alphabetical surname convention would tend to dilute the overall difference in gender ratio between first and last authors, meaning that the true difference in gender ratio between early career and senior researchers might be greater than our results suggest."
Causes: (1) demographic inertia (number of women graduates was lower in the past), (2) leaky pipeline (greater number of women than men leave academia at particular junctures), (3) women may progress to research leadership roles more slowly than men, (4) Discussion over authorship may be influenced by gender (women are less likely to be offered, or to request, the last author position). "Indeed, the National Academies of Science, Engineering, and Medicine (US) concluded that the deficit of women in STEMM is not because too few women enter the field or because women are less committed to their STEMM careers, but rather because assumptions and stereotypes about gender operate in personal interactions, evaluative processes and departmental cultures that systematically impede women's career advancement in academic medicine, science and engineering." "Worryingly, highly male-biased disciplines tended to show slow improvement in the gender ratio with time [...] Thus, novel interventions appear necessary if we are to make progress in strongly gender-biased disciplines."
"Among the major research-producing countries, the STEMM gender gap was especially pronounced in Japan, Germany, and Switzerland. The most gender-equitable countries spanned Europe, Souther America, and Africa. [...] countries in which children of both sexes attend school longer have more women authors, while countries with higher per capita income have fewer women authors. [...] Though correlational, these results imply that wealth does not necessarily diminish gender inequality in the STEMM workforce, though access to education might. Cultural and historical factors are challenging to meaningfully capture in this type of analysis, but we suspect that they play a major role."
"Journal impact factor (standardized by discipline) negatively correlated with the proportion of women authors. Review-focused journals also had fewer women authors than non-review-focused journals, and there were more women authors in OA [Open-Access] than non-OA journals, particularly within review journals. These results imply that women are disadvantaged and suggest remedial strategies. Prestigious journals tend to reject many submissions without peer review, and editors are usually aware of authors' names (and thus genders), even for journals that use double-blind peer review. Gender bias has been implicated in non experimental studies of peer review and experimentally demonstrated in other academic contexts, suggesting a need for double-blind editing and review." "We hypothesized that women may be invited to submit academic papers less often than men, given that this is the case for invited keynote lectures at some conferences. [...] we estimate that men are 1.7-2.1 times more likely than women to be invited to submit papers. The gender ratio among authors of invited papers is more male-biased than the gender ratio of last authors or single authors. This suggests a need to scrutinize editorial practices, appoint women editors, and implement gender targets when using an invitation-based publishing model."
"Another explanation for the elevated gender disparity we observed in higher-impact journals is that women submit a lower proportion of their manuscripts to prestigious journals. A recent study, upon finding that women's papers passed peer review more frequently than men's, hypothesized that women practice 'better targeting of papers to a journal'. A more pessimistic hypothesis is that women are not encouraged to aim high by colleagues and mentors or do not try because they believe themselves to have a lower chance of success. These issues could be addressed via mentoring programs for staff and team leaders and by taking steps to promote women role models. Because the variables examined here all potentially affect citation rate, our results partially explain previous reports that women's papers are cited less often than same-discipline papers written by men. The 'citation gap' would likely shrink if barriers to women publishing highly visible papers, e.g., invited review in prestigious journals, were removed."
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