Galaxy Zoo Talk

total galaxy mass over time

  • liometopum by liometopum

    1. When I look at the SDSS galaxy map, showing the distribution of galaxies, it appears that the number of galaxies is constant over time (distance from us).
    2. But the younger, more distant, galaxies are smaller.

    So... is the total of the mass of all galaxies increasing over time?
    And, are there any papers published talking about this?

    Posted

  • Budgieye by Budgieye moderator

    Are galaxies getting bigger? Yes. This is a hard question, and I was hoping a scientist would answer.

    Younger and more distant galaxies are smaller. Distance=younger, as we are looking back in time when we look at distant galaxies. Over periods of billions of years, small galaxies attract each other, and merge together, forming bigger galaxies.

    So there is still the same amount of mass in the galaxies, but it is concentrated into bigger galaxies. I will look for a publication to support this. Try http://en.wikipedia.org/wiki/Galaxy_formation_and_evolution for now.

    It may get more complicated than that. Possibly stretching space causes new mass to pop into existence, but this is probably not what you are thinking about.

    Posted

  • liometopum by liometopum

    "It may get more complicated than that. Possibly stretching space causes new mass to pop into existence, but this is probably not what you are thinking about.".... actually, it is what I was thinking about! Standard theory is that all matter was created at the time of the BB, but I think it is being continually created, as space expands. (I can provide numbers if needed)
    It seems like the galaxy density is roughly the same over time, but the mass of galaxies increases with time, indicating total mass is increasing. Galaxies might provide an estimation of mass change over time.

    Does anyone have thoughts on this?

    Posted

  • JeanTate by JeanTate in response to liometopum's comment.

    I think it would be quite difficult to make a robust case that the spatial density of galaxies has changed much over the time represented by redshift 0.25 to 0, using only SDSS data; it's a fairly small fraction of the time since the surface of last scattering (i.e. when photons streamed free, z ~1100), and I don't think the SDSS selection biases are well enough constrained.

    So... is the total of the mass of all galaxies increasing over time? And, are there any papers published talking about this?

    I think it's difficult to answer this question, without first working out, carefully, what you mean by "the total of the mass of all galaxies". For example, the mass of almost all 'non-dwarf' galaxies is currently thought to be dominated by dark matter, but I think you may have been thinking 'baryonic (ordinary) mass', or perhaps just 'mass in the form of stars'. Then there's the question of what's a galaxy and what's not ...

    An interesting recent paper that bears on this last question is Cantiello+ (2014), "VEGAS-SSS. A VST survey of elliptical galaxies in the southern hemisphere: analysis of small stellar systems. Testing the methodology on the globular cluster system in NGC3115"

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  • mlpeck by mlpeck in response to liometopum's comment.

    Standard theory is that all matter was created at the time of the BB,
    but I think it is being continually created, as space expands.

    Continuous creation of matter was the essential feature of Fred Hoyle's Steady State model, which lost out to the big bang when the cosmic microwave background was discovered.

    Posted

  • liometopum by liometopum

    Yes, the distance is short. My own math indicates that the total mass at z = 0.1 would be about 88% of current mass. So maybe that could be measured. The SDSS maps includes distances, so somebody may have calculated how many galaxies exist at each unit distance from us. It seems such an obvious thing to do.

    Mlpeck, the Hoyle Steady State has continuous creation as part of it, but no BB. You can model expansion using the continuous creation of matter starting from the BB.

    If you calculate the number of elementary particles in the observable universe,you get a number of about 10^81. That is actually a really interesting number. Scott Funkhouser published a paper, http://arxiv.org/ftp/physics/papers/0611/0611115.pdf talking about a new large number, 10^122.

    Notice that the number of particles is Funkhouser's large number to the 2/3 power. Funkhouser's number is linked to the size of the universe, indicating that both values increase with time.

    Posted

  • zutopian by zutopian

    The above posts had been done in Dec 2014.

    Here is a new paper.:

    The Evolution of Galaxy Number Density at z < 8 and its Implications

    The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass functions up to z∼8 to determine how the number densities of galaxies changes as a function of time and mass limit. (...)
    We discuss the implications for these results for galaxy evolution, as well as compare our results with the latest models of galaxy formation. These results also reveal that the cosmic background light in the optical and near-infrared likely arise from these unobserved faint galaxies. We also show how these results solve the question of why the sky at night is dark, otherwise known as Olbers' paradox.

    Authors: Christopher J. Conselice, Aaron Wilkinson, Kenneth Duncan, Alice Mortlock
    (Submitted on 13 Jul 2016)
    http://arxiv.org/abs/1607.03909

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