How can a galaxy accumulate more gas

This fate awaits only those stars with a mass up to about 1. Above that mass, electron pressure cannot support the core against further collapse. Such stars suffer a different fate as described below. White Dwarfs May Become Novae If a white dwarf forms in a binary or multiple star system, it may experience a more eventful demise as a nova.

Nova is Latin for "new" - novae were once thought to be new stars. Today, we understand that they are in fact, very old stars - white dwarfs. If a white dwarf is close enough to a companion star, its gravity may drag matter - mostly hydrogen - from the outer layers of that star onto itself, building up its surface layer.

When enough hydrogen has accumulated on the surface, a burst of nuclear fusion occurs, causing the white dwarf to brighten substantially and expel the remaining material. Within a few days, the glow subsides and the cycle starts again. Sometimes, particularly massive white dwarfs those near the 1. Supernovae Leave Behind Neutron Stars or Black Holes Main sequence stars over eight solar masses are destined to die in a titanic explosion called a supernova. A supernova is not merely a bigger nova.

In a nova, only the star's surface explodes. In a supernova, the star's core collapses and then explodes. In massive stars, a complex series of nuclear reactions leads to the production of iron in the core. Having achieved iron, the star has wrung all the energy it can out of nuclear fusion - fusion reactions that form elements heavier than iron actually consume energy rather than produce it.

The star no longer has any way to support its own mass, and the iron core collapses. In just a matter of seconds the core shrinks from roughly miles across to just a dozen, and the temperature spikes billion degrees or more. The outer layers of the star initially begin to collapse along with the core, but rebound with the enormous release of energy and are thrown violently outward.

Supernovae release an almost unimaginable amount of energy. For a period of days to weeks, a supernova may outshine an entire galaxy. Likewise, all the naturally occurring elements and a rich array of subatomic particles are produced in these explosions.

On average, a supernova explosion occurs about once every hundred years in the typical galaxy. About 25 to 50 supernovae are discovered each year in other galaxies, but most are too far away to be seen without a telescope. Neutron Stars If the collapsing stellar core at the center of a supernova contains between about 1.

Neutron stars are incredibly dense - similar to the density of an atomic nucleus. Because it contains so much mass packed into such a small volume, the gravitation at the surface of a neutron star is immense. Animals Wild Cities Wild parakeets have taken a liking to London. Animals Wild Cities Morocco has 3 million stray dogs. Meet the people trying to help. Environment COP26 nears conclusion with mixed signals and frustration. Environment Planet Possible India bets its energy future on solar—in ways both small and big.

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Our main results can be summarized as follows. The predictions for the K - and b J -band LFs and for the stellar mass function are in good agreement with observations. In particular, the number density of dwarfs is reproduced with greater accuracy than in the model presented in DLB The stellar mass—stellar metallicity and the luminosity—gas metallicity relationships are in good agreement with observations and significantly improve previous results.

Again, the improvement is significant for dwarf galaxies. These results demonstrate that in our model the treatment of feedback in dwarf galaxies is significantly improved with respect to previous implementations. We argue that the main reason for this improvement is the possibility of estimating the amount of mass and metals that a halo can permanently lose and deposit into the IGM. This feature determines a stronger quenching of star formation in small haloes and therefore the suppression of the faint end of the stellar mass and LFs of galaxies, and the shape of the mass—stellar metallicity and of the luminosity—gas metallicity relationships.

Our model, however, also exhibits some weaknesses. First, there is a tendency to overestimate the number of bright galaxies in the LFs, because of the continuous recycling of gas when winds recollapse in massive haloes. A possible solution could be an increase in the efficiency of AGN feedback about 20—30 per cent more intense than suggested by Croton et al. Finally, perhaps the most severe shortcoming of the model is that it does not correctly reproduce the colour distribution of galaxies.

In particular, our model results do not exhibit the sharp colour bimodality observed for galaxies in the local universe. This feature does not depend on the specific values of the model parameters and it can be alleviated only by assuming very inefficient feedback. However, models with inefficient feedback do not correctly reproduce the abundance of dwarf galaxies, nor their metallicities.

In the second part of our paper, we have investigated the efficiency of the mass and metal injection in winds and their deposition into the IGM. Larger haloes like groups and clusters lose only a small fraction of their mass and metals, and this occurs before most of the halo mass is accreted. Our feedback model contains the same number of free parameters i. The numerical calculation of the evolution of winds is only slightly more time consuming than previous feedback schemes.

However, it does require about 10—15 per cent additional memory to handle the wind variables and to store them on disc, if desired. We would like to thank Jon Loveday and Bernard Pagel for useful discussions and Simon White for reading the manuscript. We also thank the referee, Pierluigi Monaco, for his insightful suggestions that helped to improve the quality of the paper.

Adelberger K. Shapley A. Steidel C. Pettini M. Erb D. Reddy N. Aguirre A. Hernquist L. Schaye J. Katz N. Weinberg D. Gardner J. Kim T. Theuns T. Rauch M. Sargent W. Asplund M. Grevesse N. Sauval A. Bell E. McIntosh D. Weinberg M. Benson A. Bower R. Frenk C. Lacey C. Baugh C. Cole S. Bertone S. Stoehr F. White S. Lehnert M. Peroux C. Bergeron J. Malbon R. Helly J. Chabrier G. Cecil G. Bland-Hawthorn J. Veilleux S. Filippenko A.

Charlot S. Longhetti M. Coles S. Conselice C. Croton D. Daigne F. Olive K. Silk J. Vangioni E. Dekel A. Delahaye F. Pinsonneault M.

De Lucia G. Kauffmann G. Springel V. Blaizot J. De Vaucouleurs G. De Vaucouleurs A. Corwin H. Buta R. Paturel G. Fouque P. Google Scholar. Google Preview. Di Matteo T. Edmunds M. Pagel B. Frye B. Broadhurst T. Benitez N. Gallazzi A. Brinchmann J. Tremonti C. Garnett D. Heckman T. Strickland D. Armus L. Jones D. Peterson B. Colless M. Saunders W. A simple isothermal gas sphere would suggest constant shell mass, or.

The overall results discussed throughout this paper are not significantly affected by the choice of. For instance, the fraction of gas-poor galaxies changes by less than 0. If there are no external gas blobs detected within 6 R 90 of the galaxy, the boundary of the region of interest is set to 6 R 90 , which is typically greater than kpc at redshift zero and roughly comparable with the virial radius of the galaxy.

We describe below how the galactic gas and ambient medium were separated from the chunk of gas within this region. In real galaxies, the ISM can have multiple phases, from the hot, ionized medium , to extremely cold and dense molecular clouds ,. In this study, we define "galactic cold gas" as gas cells roughly in hydrostatic equilibrium, cooled and settled down at.

The blue dashed contour in Figure 2 shows the distribution of cold gas cells of an example galaxy. The gas cells with densities greater than 0. In general, the ambient gas cells have low metallicities compared to the metal-enriched galactic gas cells. Large H i surveys of the galaxies in the local universe have reported an anticorrelation between the gas fraction and stellar mass Catinella et al. The scaling relation extends to the galaxies in cluster environments but with an offset toward the lower gas fraction Cortese et al.

These galaxies are the ones not affected by dense environments, and we confirm that they reveal a similar sequence on the plane blue shades in Figure 3. Figure 3. The gray dots are the galaxies at redshift zero. Colored lines are the gas fraction from H i observations Catinella et al. In this study, we classify a galaxy as "gas poor" when it sufficiently deviates from this gas-rich galaxy sequence toward the lower side. Observations have reported that gas-poor galaxies are most common near the central region of clusters and their fraction steadily declines farther outward, extending far beyond several virial radii of the cluster e.

The distribution of gas-poor galaxies is the final result of a combination of various gas-depletion processes acting inside and outside clusters. Our sample galaxies also show the steady decline of the fraction of gas-poor galaxies starting from the cluster center out to 3 R see the gray line in Figure 4. In this section, we investigate the radial distribution of gas-poor galaxies in order to examine the mechanisms responsible for the gas depletion in our sample galaxies.

Figure 4. Among the first infallers, galaxies that have always been central galaxies, that is, ones that have never been affected by the group environmental effect, are shown in purple. We find evidence of both cluster environmental effects and preprocessing on the galaxies falling into clusters see text for detailed discussion.

Based on whether or not a galaxy passed its first pericenter within a cluster, we separate our sample into "first-infall" blue color and "post-first-pericentric pass" hereafter PFPP, orange color populations. Here, the first pericenter of the orbit is defined as the point where a velocity vector of a galaxy and a direction vector toward the cluster center are perpendicular for the first time.

For galaxies approaching cluster centers for the first time, their radial distances from the centers roughly correspond to their time since infall e. Therefore, by investigating the first-infall population, we can explore the significance of the environmental effect of the cluster as well as preprocessing effects. On the contrary, PFPP galaxies are the ones that have already gone through multiple pericentric passages and sunk down to the central region of the cluster.

Within 1. This strongly suggests that galaxies gradually become gas deficient in their first approach to the cluster center, providing clear evidence for the cluster environmental effect. This topic will be discussed further in Section 5. Meanwhile, at a distance between 1. It is important to note that the effect of group preprocessing is visible among the galaxies in this distance range.

The purple line shows the fraction of gas-poor galaxies among the galaxies that have never been a satellite of any halo over their lifetime these galaxies are a subsample of the first infalling population. In other words, they have always been a "central" galaxy. In other words, galaxies that pass through the group environment are more likely to become depleted in their gas compared to those who have always been a central galaxy.

This topic will be discussed in detail in Section 4. We now focus on the origin of the radial trend of the whole sample gray line in the outer region 1.

To begin with, the radial trend of the fraction of gas-poor galaxies among the first infalling galaxies blue shade is notably weakened at a distance larger than 1. This implies that the cluster environmental effect is not strong until a galaxy falls inside a cluster see also Wetzel et al.

On the other hand, PFPP galaxies are almost completely gas poor regardless of their distance from the cluster center see orange line. Note that the orange histogram in panel b shows the radial distribution of PFPP galaxies. In contrast, some PFPP galaxies with elongated orbits easily reach beyond the virial radius. PFPP galaxies hardly reach distances larger than 2. As a consequence, even though there is no radial trend among the first infalling galaxies beyond 1.

The overall radial trend of gas-poor galaxy fraction is a result of the combination of preprocessing and cluster processing effects. Based on the discussions made in this section, we explore each process in detail in the following Sections 4 and 5. In this section, we investigate the significance of preprocessing effects in detail. We define "preprocessed galaxy" as a galaxy that becomes "gas poor" see Section 2.

Therefore, the preprocessing indicates the integrated effect of unspecified mechanisms that induce gas depletion before the cluster entry.

Preprocessed galaxies may be replenished with cold gas afterward, but we find replenishment to be rare in our simulation. This can be attributed to the fact that virialized hot gas cools inefficiently in the massive halos. In the case of satellites, the ram pressure stripping continuously prevents the gas from collapsing onto the galaxies.

In addition, even when a galaxy is rejuvenated, we find that it normally lasts less than a gigayear, and the majority of the rejuvenated galaxies return to the gas-poor state before they reach 1. The significance of preprocessing has been a controversial issue. Assuming that dark matter halos of mass greater than host a galaxy, Berrier et al. For clusters with a mass range of , they argued that preprocessing is uncommon.

On the contrary, using the galform semianalytic model of galaxy formation, McGee et al. Their sample covered massive clusters up to , and they discovered that galaxies are more likely to be preprocessed in more massive clusters. It is true that galaxies in more massive groups have a higher chance of being in a gas-deficient state, but this hypothesis may misestimate the fraction of preprocessed galaxies in the following circumstances.

In the real universe, not all galaxies within massive halos are gas deficient, and at the same time, some gas-poor galaxies are not associated with a group at the moment of the cluster infall. The former occurs when a satellite does not spend sufficient time to experience the group environment.

The latter occurs when a satellite escapes its group halo or appears to have escaped due to its elongated orbit after spending sufficient time to suffer the gas depletion. Therefore, instead of using the host mass at the time of the cluster infall M h,infall , another parameter should be introduced that better reflects the history of the environmental effect. In the central panel, points represent individual galaxies that have entered clusters. The red points are the preprocessed galaxies, and gray points are all of the others.

The top and right panels show the distributions of M h,infall and M h,before of the two populations. The colored regions designate the areas where M h,infall severely underestimates M h,before upper left with blue shading and where M h,infall severely overestimates M h,before lower right, green. Figure 5. The red and gray points show the preprocessed galaxies and those entering clusters with gas, respectively.

The histograms in the top and right panels show the distribution of M h,infall and M h,before of each population. The numbers in the boxes on each quadrant are the fractions of the preprocessed galaxy within each quadrant.

The preprocessed galaxy fraction correlates better with M h,before than with M h,infall. The numbers in the box in each quadrant show the fraction of preprocessed galaxies.

This highlights the shortcoming of the use of M h,infall as a criterion for preprocessing, as was the case in some previous studies. Though they are in a relatively massive group at the cluster infall moment, only a small fraction of galaxies appear to be preprocessed, mostly because they have not spent enough time in the current group halo yet. The histograms in the two panels on the top and right sum it up: M h,before separates preprocessed and non-preprocessed galaxies better, and thus we have decided to use it in our analysis.

We will now investigate the conditions for which preprocessing becomes most efficient. To see whether the preprocessing mechanism found in our simulation is due to the environmental effect, we first separate our YZiCS sample galaxies into two groups: the central and satellite infallers.

At each snapshot, we determine the central and satellite galaxies by comparing their stellar mass at that moment, so that the central galaxies are always more massive than the companion satellites within their host dark matter halo. Note that the locations of galaxies within group halos are not considered when classifying the central and satellites. The sample is then separated into "central infallers" and "satellite infallers.

The "satellite infallers" are the remaining, the galaxies that have belonged to groups as satellite galaxies before the cluster infall.

Figure 6 shows the preprocessed galaxy fraction red color and white numbers on each bin depending on the M h,before and , where is the stellar mass at the time of the infall. The sample galaxies are separated into a central infallers and b satellite infallers. The numbers on the top left of each panel show the number of preprocessed galaxies divided by the total number of galaxies that entered clusters.

The satellite infallers have an approximately seven times larger preprocessed fraction than central infallers do. Among the satellite infallers, only 30 3. The rest of them deplete their gas as group satellites. Figure 6. Fraction of preprocessed galaxies vs. M h,before and. Each panel corresponds to the a central and b satellite infallers, respectively.

The numbers on the top left of each panel show the number of preprocessed galaxies over the total number of galaxies entering the clusters.

The satellite infallers have seven times higher preprocessed fractions compared with the central infallers. The red color and numbers on each bin are the fraction of the preprocessed galaxies within the bin.

This seems natural because galaxies in more massive halos undergo stronger ram pressure as they normally go through a denser intragroup medium with a higher orbital velocity.

At the same time, considering that gas stripping through ram pressure is achieved through a competition between ram pressure and gravitational restoring force, lower mass galaxies lose their gas more efficiently under the equal intensity of ram pressure. The importance of and caveats on this issue will be discussed more in Section 6. This result of more massive galaxies having a higher chance of containing cold gas is seemingly in conflict with the concept of "mass quenching" e.

However, in the following discussion, we confirm that this is not the case. Figure 7 shows the fraction of gas-poor galaxies vs. The green and blue lines represent galaxies that have been satellites of larger groups and galaxies that have always been central galaxies, respectively. By separating these two populations, we find opposite trends.

As discussed above, satellite galaxies more efficiently become gas deficient when their stellar mass is small. Conversely, central galaxies show increased gas-poor galaxy fractions with increasing stellar mass, which agrees with the expectation from mass quenching. That is, we verify that there is an indication of the mass effect among our YZiCS galaxies, but the environmental effect that is more efficient for low-mass galaxies overturns the trend.

Besides, the distinction between central and satellite galaxies gets weaker when considering massive galaxies. Their results are all consistent with our simulation. Figure 7. Fraction of gas-poor galaxies as a function of stellar mass. Only the galaxies that have not yet fallen into clusters until redshift zero are presented. Of the galaxies that have always been central galaxies blue , more massive galaxies are more likely to be gas poor.

This trend agrees with the concept of "mass quenching. Now we examine the preprocessed fraction of each cluster separately to see whether there are any indications of a correlation between the preprocessed fraction and cluster properties. As shown in the previous section, the amount of preprocessed galaxies is linked with how many galaxies underwent the environmental effect in the massive group-size halos before the cluster infall.

For clusters that accreted a larger number of massive groups and their constituent galaxies, a higher preprocessed galaxy fraction is expected see panel a of Figure 8. For each cluster, we measure the arithmetic average of M h,before of cluster member galaxies to estimate the representative degree of the environmental effect before falling into the clusters.